PHP Tutorial

This tutorial is free and design for educational purpose only. If you have any enquiry contact us at tutorial@isolutionsynergyideas.com

The PHP Hypertext Preprocessor (PHP) is a programming language that allows web developers to create dynamic content that interacts with databases. PHP is basically used for developing web based software applications. This tutorial helps you to build your base with PHP.

This tutorial is designed for PHP programmers who are completely unaware of PHP concepts but they have basic understanding on computer programming.

PHP code example:

									

This code will display: "Hello, PHP!"

<html> <head> <title>PHP Code Example</title> </head> <body> <?php echo "<h1>Hello, PHP!</h1>"; ?> </body> </html>

PHP started out as a small open source project that evolved as more and more people found out how useful it was. Rasmus Lerdorf unleashed the first version of PHP way back in 1994.

  • PHP is a recursive acronym for "PHP: Hypertext Preprocessor".
  • PHP is a server side scripting language that is embedded in HTML. It is used to manage dynamic content, databases, session tracking, even build entire e-commerce sites.
  • It is integrated with a number of popular databases, including MySQL, PostgreSQL, Oracle, Sybase, Informix, and Microsoft SQL Server.
  • PHP is pleasingly zippy in its execution, especially when compiled as an Apache module on the Unix side. The MySQL server, once started, executes even very complex queries with huge result sets in record-setting time.
  • PHP supports a large number of major protocols such as POP3, IMAP, and LDAP. PHP4 added support for Java and distributed object architectures (COM and CORBA), making n-tier development a possibility for the first time.
  • PHP is forgiving: PHP language tries to be as forgiving as possible.
  • PHP Syntax is C-Like.

Common uses of PHP

  1. PHP performs system functions, i.e. from files on a system it can create, open, read, write, and close them.
  2. PHP can handle forms, i.e. gather data from files, save data to a file, thru email you can send data, return data to the user.
  3. You add, delete, modify elements within your database thru PHP.
  4. Access cookies variables and set cookies.
  5. Using PHP, you can restrict users to access some pages of your website.
  6. It can encrypt data.

Common uses of PHP

    Five important characteristics make PHP's practical nature possible

  1. Simplicity
  2. Efficiency
  3. Security
  4. Flexibility
  5. Familiarity

"Hello World" Script in PHP

To get a feel for PHP, first start with simple PHP scripts. Since "Hello, World!" is an essential example, first we will create a friendly little "Hello, World!" script.

As mentioned earlier, PHP is embedded in HTML. That means that in amongst your normal HTML (or XHTML if you're cutting-edge) you'll have PHP statements like this

<html>
   <head>
      <title>Hello World</title>
   </head>
   
   <body>
      <?php echo "Hello, World!";?>
   </body>

</html>

It will produce following result:

   Hello, World!
									

If you examine the HTML output of the above example, you'll notice that the PHP code is not present in the file sent from the server to your Web browser. All of the PHP present in the Web page is processed and stripped from the page; the only thing returned to the client from the Web server is pure HTML output.

All PHP code must be included inside one of the three special markup tags that are recognised by the PHP Parser.

<?php PHP code goes here ?>

<?    PHP code goes here ?>

<script language="php"> PHP code goes here </script>

A most common tag is the <?php...?> and we will also use the same tag in our tutorial.

From the next chapter we will start with PHP Environment Setup on your machine and then we will dig out almost all concepts related to PHP to make you comfortable with the PHP language.

In order to develop and run PHP Web pages three vital components need to be installed on your computer system.

  1. Web Server − PHP will work with virtually all Web Server software, including Microsoft's Internet Information Server (IIS) but then most often used is freely available Apache Server. Download Apache for free here − http://httpd.apache.org/download.cgi
  2. Database − PHP will work with virtually all database software, including Oracle and Sybase but most commonly used is freely available MySQL database. Download MySQL for free here − http://www.mysql.com/downloads/
  3. PHP Parser − In order to process PHP script instructions a parser must be installed to generate HTML output that can be sent to the Web Browser. This tutorial will guide you how to install PHP parser on your computer.

PHP Parser Installation

Before you proceed it is important to make sure that you have proper environment setup on your machine to develop your web programs using PHP.

Type the following address into your browser's address box.

http://127.0.0.1/info.php

If this displays a page showing your PHP installation related information then it means you have PHP and Webserver installed properly. Otherwise you have to follow given procedure to install PHP on your computer.

This section will guide you to install and configure PHP over the following four platforms:

  1. PHP - Installation on Linux/Unix: If you plan to install PHP on Linux or any other variant of Unix, then here is the list of prerequisites:
    1. The PHP source distribution http://www.php.net/downloads.php
    2. The latest Apache source distribution http://httpd.apache.org/download.cgi
    3. A working PHP-supported database, if you plan to use one ( For example MySQL, Oracle etc. )
    4. Any other supported software to which PHP must connect (mail server, BCMath package, JDK, and so forth)
    5. An ANSI C compiler
    6. Gnu make utility − you can freely download it at http://www.gnu.org/software/make

    Now here are the steps to install Apache and PHP5 on your Linux or Unix machine. If your PHP or Apache versions are different then please take care accordingly.

    1. If you haven't already done so, unzip and untar your Apache source distribution. Unless you have a reason to do otherwise, /usr/local is the standard place.
      gunzip -c apache_1.3.x.tar.gz
      tar -xvf apache_1.3.x.tar
    2. Build the apache Server as follows:
      cd apache_1.3.x
      ./configure --prefix=/usr/local/apache --enable-so
      make
      make install
    3. Unzip and untar your PHP source distribution. Unless you have a reason to do otherwise, /usr/local is the standard place.
      gunzip -c php-5.x.tar.gz
      tar -xvf php-5.x.tar
      cd php-5.x
    4. Configure and Build your PHP, assuming you are using MySQL database.
      ./configure --with-apxs=/usr/sbin/apxs \
      	--with-mysql=/usr/bin/mysql
      make
      make install
    5. Install the php.ini file. Edit this file to get configuration directives
      cd ../../php-5.x
      cp php.ini-dist /usr/local/lib/php.ini
    6. Tell your Apache server where you want to serve files from, and what extension(s) you want to identify PHP files A .php is the standard, but you can use .html, .phtml, or whatever you want.
      1. Go to your HTTP configuration files (/usr/local/apache/conf or whatever your path is)
      2. Open httpd.conf with a text editor.
      3. Search for the word DocumentRoot (which should appear twice), and change both paths to the directory you want to serve files out of (in our case, /home/httpd). We recommend a home directory rather than the default /usr/local/apache/htdocs because it is more secure, but it doesn.t have to be in a home directory. You will keep all your PHP files in this directory.
    7. Add at least one PHP extension directive, as shown in the first line of code that follows. In the second line, we.ve also added a second handler to have all HTML files parsed as PHP.
    8. AddType application/x-httpd-php .php
      AddType application/x-httpd-php .html
    9. Restart your server. Every time you change your HTTP configuration or php.ini files, you must stop and start your server again.
    10. cd ../bin
      ./apachectl start
    11. Set the document root directory permissions to world-executable. The actual PHP files in the directory need only be world-readable (644). If necessary, replace /home/httpd with your document root below:
    12. chmod 755 /home/httpd/html/php
    13. Open a text editor. Type: <?php phpinfo(); ?>. Save this file in your Web server's document root as info.php.
    14. Start any Web browser and browse the file.you must always use an HTTP request (http://www.testdomain.com/info.php or http://localhost/info.php or http://127.0.0.1/info.php) rather than a filename (/home/httpd/info.php) for the file to be parsed correctly

    You should see a long table of information about your new PHP installation message Congratulations!

  2. PHP - Installation on Mac OS X

    Mac users have the choice of either a binary or a source installation. In fact, your OS X probably came with Apache and PHP preinstalled. This is likely to be quite an old build, and it probably lacks many of the less common extensions.

    However, if all you want is a quick Apache + PHP + MySQL/PostgreSQL setup on your laptop, this is certainly the easiest way to fly. All you need to do is edit your Apache configuration file and turn on the Web server.

    So just follow the following steps:

    1. Open the Apache config file in a text editor as root.
      sudo open -a TextEdit /etc/httpd/httpd.conf
    2. Edit the file. Uncomment the following lines
      Load Module php5_module
      AddModule mod_php5.c
      AddType application/x-httpd-php .php
    3. You may also want to uncomment the block or otherwise tell Apache which directory to serve out of.
    4. Restart the Web server
      sudo apachectl graceful
    5. Open a text editor. Type: <?php phpinfo(); ?>. Save this file in your Web server's document root as info.php.
    6. Start any Web browser and browse the file.you must always use an HTTP request (http://www.testdomain.com/info.php or http://localhost/info.php or http://127.0.0.1/info.php) rather than a filename (/home/httpd/info.php) for the file to be parsed correctly

    You should see a long table of information about your new PHP installation message Congratulations!

  3. PHP - Installation on Windows with IIS

    The Windows server installation of PHP running IIS is much simpler than on Unix, since it involves a precompiled binary rather than a source build.

    If you plan to install PHP over Windows, then here is the list of prerequisites:

    1. A working PHP-supported Web server. Under previous versions of PHP, IIS/PWS was the easiest choice because a module version of PHP was available for it; but PHP now has added a much wider selection of modules for Windows.
    2. A correctly installed PHP-supported database like MySQL or Oracle etc. (if you plan to use one)
    3. The PHP Windows binary distribution (download it at www.php.net/downloads.php)
    4. A utility to unzip files (search http://download.cnet.com for PC file compression utilities)

    Now here are the steps to install Apache and PHP5 on your Windows machine. If your PHP version is different then please take care accordingly.

    1. Extract the binary archive using your unzip utility; C:\PHP is a common location.
    2. Copy some .dll files from your PHP directory to your systems directory (usually C:\Winnt\System32). You need php5ts.dll for every case. You will also probably need to copy the file corresponding to your Web server module - C:\PHP\Sapi\php5isapi.dll. It's possible you will also need others from the dlls subfolder - but start with the two mentioned above and add more if you need them.
    3. Copy either php.ini-dist or php.ini-recommended (preferably the latter) to your Windows directory (C:\Winnt or C:\Winnt40), and rename it php.ini. Open this file in a text editor (for example, Notepad). Edit this file to get configuration directives; We highly recommend new users set error reporting to E_ALL on their development machines at this point. For now, the most important thing is the doc_root directive under the Paths and Directories section.make sure this matches your IIS Inetpub folder (or wherever you plan to serve out of).
    4. Stop and restart the WWW service. Go to the Start menu → Settings → Control Panel → Services. Scroll down the list to IIS Admin Service. Select it and click Stop. After it stops, select World Wide Web Publishing Service and click Start. Stopping and restarting the service from within Internet Service Manager will not suffice. Since this is Windows, you may also wish to reboot.
    5. Open a text editor. Type: <?php phpinfo(); ?>. Save this file in your Web server's document root as info.php.
    6. Start any Web browser and browse the file.you must always use an HTTP request (http://www.testdomain.com/info.php or http://localhost/info.php or http://127.0.0.1/info.php) rather than a filename (/home/httpd/info.php) for the file to be parsed correctly

    You should see a long table of information about your new PHP installation message Congratulations!

  4. PHP - Installation on Windows with Apache

    To install Apache with PHP 5 on Windows follow the following steps. If your PHP and Apache versions are different then please take care accordingly.

    1. Download Apache server from www.apache.org/dist/httpd/binaries/win32. You want the current stable release version with the no_src.msi extension. Double-click the installer file to install; C:\Program Files is a common location. The installer will also ask you whether you want to run Apache as a service or from the command line or DOS prompt. We recommend you do not install as a service, as this may cause problems with startup.
    2. Extract the PHP binary archive using your unzip utility; C:\PHP is a common location.
    3. Copy some .dll files from your PHP directory to your system directory (usually C:\Windows). You need php5ts.dll for every case. You will also probably need to copy the file corresponding to your Web server module - C:\PHP\Sapi\php5apache.dll. to your Apache modules directory. It's possible that you will also need others from the dlls subfolder.but start with the two mentioned previously and add more if you need them.
    4. Copy either php.ini-dist or php.ini-recommended (preferably the latter) to your Windows directory, and rename it php.ini. Open this file in a text editor (for example, Notepad). Edit this file to get configuration directives; At this point, we highly recommend that new users set error reporting to E_ALL on their development machines.
    5. Tell your Apache server where you want to serve files from and what extension(s) you want to identify PHP files (.php is the standard, but you can use .html, .phtml, or whatever you want). Go to your HTTP configuration files (C:\Program Files\Apache Group\Apache\conf or whatever your path is), and open httpd.conf with a text editor. Search for the word DocumentRoot (which should appear twice) and change both paths to the directory you want to serve files out of. (The default is C:\Program Files\Apache Group\Apache\htdocs.). Add at least one PHP extension directive as shown in the first line of the following code
    6. LoadModule php5_module modules/php5apache.dll
      AddType application/x-httpd-php .php .phtml
    7. You may also need to add the following line
    8. AddModule mod_php5.c
    9. Stop and restart the WWW service. Go to the Start menu → Settings → Control Panel → Services. Scroll down the list to IIS Admin Service. Select it and click Stop. After it stops, select World Wide Web Publishing Service and click Start. Stopping and restarting the service from within Internet Service Manager will not suffice. Since this is Windows, you may also wish to reboot.
    10. Open a text editor. Type: <?php phpinfo(); ?>. Save this file in your Web server's document root as info.php.
    11. Start any Web browser and browse the file.you must always use an HTTP request (http://www.testdomain.com/info.php or http://localhost/info.php or http://127.0.0.1/info.php) rather than a filename (/home/httpd/info.php) for the file to be parsed correctly

    You should see a long table of information about your new PHP installation message Congratulations!

Apache Configuration

If you are using Apache as a Web Server then this section will guide you to edit Apache Configuration Files.

Apache uses httpd.conf file for global settings, and the .htaccess file for per-directory access settings. Older versions of Apache split up httpd.conf into three files (access.conf, httpd.conf, and srm.conf), and some users still prefer this arrangement.

The following section describe settings in httpd.conf that affect PHP directly and cannot be set elsewhere. If you have standard installation then httpd.conf will be found at /etc/httpd/conf:

Timeout

This value sets the default number of seconds before any HTTP request will time out. If you set PHP's max_execution_time to longer than this value, PHP will keep grinding away but the user may see a 404 error. In safe mode, this value will be ignored; you must use the timeout value in php.ini instead

DocumentRoot

DocumentRoot designates the root directory for all HTTP processes on that server. It looks something like this on Unix

DocumentRoot ./usr/local/apache_1.3.6/htdocs.

You can choose any directory as document root.

AddType

The PHP MIME type needs to be set here for PHP files to be parsed. Remember that you can associate any file extension with PHP like .php3, .php5 or .htm.

AddType application/x-httpd-php .php
AddType application/x-httpd-phps .phps
AddType application/x-httpd-php3 .php3 .phtml
AddType application/x-httpd-php .html

Action

You must uncomment this line for the Windows apxs module version of Apache with shared object support

LoadModule php4_module modules/php4apache.dll

r on Unix flavors

LoadModule php4_module modules/mod_php.so

AddModule

You must uncomment this line for the static module version of Apache.

AddModule mod_php4.c

PHP.INI File Configuration

The PHP configuration file, php.ini, is the final and most immediate way to affect PHP's functionality.

The PHP configuration file, php.ini, is the final and most immediate way to affect PHP's functionality. The php.ini file is read each time PHP is initialized.in other words, whenever httpd is restarted for the module version or with each script execution for the CGI version. If your change isn.t showing up, remember to stop and restart httpd. If it still isn.t showing up, use phpinfo() to check the path to php.ini.

The configuration file is well commented and thorough. Keys are case sensitive, keyword values are not; whitespace, and lines beginning with semicolons are ignored. Booleans can be represented by 1/0, Yes/No, On/Off, or True/False. The default values in php.ini-dist will result in a reasonable PHP installation that can be tweaked later.

Here we are explaining the important settings in php.ini which you may need for your PHP Parser.

short_open_tag = Off

Short open tags look like this: <? ?>. This option must be set to Off if you want to use XML functions.

safe_mode = Off

If this is set to On, you probably compiled PHP with the --enable-safe-mode flag. Safe mode is most relevant to CGI use. See the explanation in the section "CGI compile-time options". earlier in this chapter.

safe_mode_exec_dir = [DIR]

This option is relevant only if safe mode is on; it can also be set with the --with-exec-dir flag during the Unix build process. PHP in safe mode only executes external binaries out of this directory. The default is /usr/local/bin. This has nothing to do with serving up a normal PHP/HTML Web page.

safe_mode_allowed_env_vars = [PHP_]

This option sets which environment variables users can change in safe mode. The default is only those variables prepended with "PHP_". If this directive is empty, most variables are alterable.

safe_mode_protected_env_vars = [LD_LIBRARY_PATH]

This option sets which environment variables users can't change in safe mode, even if safe_mode_allowed_env_vars is set permissively

disable_functions = [function1, function2...]

A welcome addition to PHP4 configuration and one perpetuated in PHP5 is the ability to disable selected functions for security reasons. Previously, this necessitated hand-editing the C code from which PHP was made. Filesystem, system, and network functions should probably be the first to go because allowing the capability to write files and alter the system over HTTP is never such a safe idea.

max_execution_time = 30

The function set_time_limit() won.t work in safe mode, so this is the main way to make a script time out in safe mode. In Windows, you have to abort based on maximum memory consumed rather than time. You can also use the Apache timeout setting to timeout if you use Apache, but that will apply to non-PHP files on the site too.

error_reporting = E_ALL & ~E_NOTICE

The default value is E_ALL & ~E_NOTICE, all errors except notices. Development servers should be set to at least the default; only production servers should even consider a lesser value.

error_prepend_string = [""]

With its bookend, error_append_string, this setting allows you to make error messages a different color than other text, or what have you.

warn_plus_overloading = Off

This setting issues a warning if the + operator is used with strings, as in a form value.

variables_order = EGPCS

This configuration setting supersedes gpc_order. Both are now deprecated along with register_globals. It sets the order of the different variables: Environment, GET, POST, COOKIE, and SERVER (aka Built-in).You can change this order around. Variables will be overwritten successively in left-to-right order, with the rightmost one winning the hand every time. This means if you left the default setting and happened to use the same name for an environment variable, a POST variable, and a COOKIE variable, the COOKIE variable would own that name at the end of the process. In real life, this doesn't happen much.

register_globals = Off

This setting allows you to decide whether you wish to register EGPCS variables as global. This is now deprecated, and as of PHP4.2, this flag is set to Off by default. Use superglobal arrays instead. All the major code listings in this book use superglobal arrays.

gpc_order = GPC

This setting has been GPC Deprecated.

magic_quotes_gpc = On

This setting escapes quotes in incoming GET/POST/COOKIE data. If you use a lot of forms which possibly submit to themselves or other forms and display form values, you may need to set this directive to On or prepare to use addslashes() on string-type data.

magic_quotes_runtime = Off

This setting escapes quotes in incoming database and text strings. Remember that SQL adds slashes to single quotes and apostrophes when storing strings and does not strip them off when returning them. If this setting is Off, you will need to use stripslashes() when outputting any type of string data from a SQL database. If magic_quotes_sybase is set to On, this must be Off.

magic_quotes_sybase = Off

This setting escapes single quotes in incoming database and text strings with Sybase-style single quotes rather than backslashes. If magic_quotes_runtime is set to On, this must be Off.

auto-prepend-file = [path/to/file]

If a path is specified here, PHP must automatically include() it at the beginning of every PHP file. Include path restrictions do apply.

auto-append-file = [path/to/file]

If a path is specified here, PHP must automatically include() it at the end of every PHP file.unless you escape by using the exit() function. Include path restrictions do apply.

include_path = [DIR]

If you set this value, you will only be allowed to include or require files from these directories. The include directory is generally under your document root; this is mandatory if you.re running in safe mode. Set this to . in order to include files from the same directory your script is in. Multiple directories are separated by colons: .:/usr/local/apache/htdocs:/usr/local/lib.

doc_root = [DIR]

If you.re using Apache, you.ve already set a document root for this server or virtual host in httpd.conf. Set this value here if you.re using safe mode or if you want to enable PHP only on a portion of your site (for example, only in one subdirectory of your Web root).

file_uploads = [on/off]

Turn on this flag if you will upload files using PHP script.

upload_tmp_dir = [DIR]

Do not uncomment this line unless you understand the implications of HTTP uploads!

session.save-handler = files

Except in rare circumstances, you will not want to change this setting. So don't touch it.

ignore_user_abort = [On/Off]

This setting controls what happens if a site visitor clicks the browser.s Stop button. The default is On, which means that the script continues to run to completion or timeout. If the setting is changed to Off, the script will abort. This setting only works in module mode, not CGI.

mysql.default_host = hostname

The default server host to use when connecting to the database server if no other host is specified.

mysql.default_user = username

The default user name to use when connecting to the database server if no other name is specified.

mysql.default_password = password

The default password to use when connecting to the database server if no other password is specified.

This chapter will give you an idea of very basic syntax of PHP and very important to make your PHP foundation strong

Escaping to PHP

The PHP parsing engine needs a way to differentiate PHP code from other elements in the page. The mechanism for doing so is known as 'escaping to PHP'. There are four ways to do this

  1. Canonical PHP tags

    The most universally effective PHP tag style is:

    <?php...?> 

    If you use this style, you can be positive that your tags will always be correctly interpreted.

  2. Short-open (SGML-style) tags

    Short or short-open tags look like this:

    <?...?> 

    Short tags are, as one might expect, the shortest option You must do one of two things to enable PHP to recognize the tags:

    1. Choose the --enable-short-tags configuration option when you're building PHP.
    2. Set the short_open_tag setting in your php.ini file to on. This option must be disabled to parse XML with PHP because the same syntax is used for XML tags.
  3. ASP-style tags

    ASP-style tags mimic the tags used by Active Server Pages to delineate code blocks. ASP-style tags look like this

    <%...%> 

    To use ASP-style tags, you will need to set the configuration option in your php.ini file.

  4. HTML script tags

    HTML script tags look like this:

    <script language="PHP">...</script> 

Commenting PHP Code

A comment is the portion of a program that exists only for the human reader and stripped out before displaying the programs result. There are two commenting formats in PHP:

  1. Single-line comments − They are generally used for short explanations or notes relevant to the local code. Here are the examples of single line comments.
    <?
       

    # This is a comment, and # This is the second line of the comment // This is a comment too. Each style comments only print "An example with single line comments";

    ?>
  2. Multi-lines comments − They are generally used to provide pseudocode algorithms and more detailed explanations when necessary. The multiline style of commenting is the same as in C. Here are the example of multi lines comments.
    <?
       /* This is a comment with multiline
          Author : Maimaje Bello Abdullahi
          Purpose: Multiline Comments Demo
          Subject: PHP
       */
       
       print "An example with multi line comments";
    ?> 
    Multi-lines printing − Here are the examples to print multiple lines in a single print statement.
    <?
       

    # First Example print <<

    This uses the "here document" syntax to output multiple lines with $variable interpolation. Note that the here document terminator must appear on a line with just a semicolon no extra whitespace! END;

    # Second Example print "This spans multiple lines. The newlines will be output as well";

    ?>

PHP is whitespace insensitive

Whitespace is the stuff you type that is typically invisible on the screen, including spaces, tabs, and carriage returns (end-of-line characters).

PHP whitespace insensitive means that it almost never matters how many whitespace characters you have in a row.one whitespace character is the same as many such characters.

For example, each of the following PHP statements that assigns the sum of 2 + 2 to the variable $four is equivalent:

$four = 2 + 2; // single spaces
$four =+2 ; // spaces and tabs
$four =
2+
2; // multiple lines

PHP is case sensitive

Yeah it is true that PHP is a case sensitive language. Try out following example:

<html>
   <body>
      
      <?php
         $capital = 67;
         print("Variable capital is $capital
"); print("Variable CaPiTaL is $CaPiTaL
"); ?> </body> </html>

This will produce the following result:

Variable capital is 67
Variable CaPiTaL is

Statements are expressions terminated by semicolons

A statement in PHP is any expression that is followed by a semicolon (;).Any sequence of valid PHP statements that is enclosed by the PHP tags is a valid PHP program. Here is a typical statement in PHP, which in this case assigns a string of characters to a variable called $greeting:

$greeting = "Welcome to PHP!";

Expressions are combinations of tokens

The smallest building blocks of PHP are the indivisible tokens, such as numbers (3.14159), strings (.two.), variables ($two), constants (TRUE), and the special words that make up the syntax of PHP itself like if, else, while, for and so forth

Braces make blocks

Although statements cannot be combined like expressions, you can always put a sequence of statements anywhere a statement can go by enclosing them in a set of curly braces.

Here both statements are equivalent:

if (3 == 2 + 1)
   print("Good - I haven't totally lost my mind.
"); if (3 == 2 + 1) { print("Good - I haven't totally"); print("lost my mind.<br>"); }

Running PHP Script from Command Prompt

Yes you can run your PHP script on your command prompt. Assuming you have following content in test.php file

<?php
   echo "Hello PHP!!!!!";
?>

Now run this script as command prompt as follows:

$ php test.php

It will produce the following result:

Hello PHP!!!!!

Hope now you have basic knowledge of PHP Syntax.

The main way to store information in the middle of a PHP program is by using a variable.

Here are the most important things to know about variables in PHP.

  1. All variables in PHP are denoted with a leading dollar sign ($).
  2. The value of a variable is the value of its most recent assignment.
  3. Variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.
  4. Variables can, but do not need, to be declared before assignment.
  5. Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.
  6. Variables used before they are assigned have default values.
  7. PHP does a good job of automatically converting types from one to another when necessary.
  8. PHP variables are Perl-like.

PHP has a total of eight data types which we use to construct our variables:

  1. Integers − are whole numbers, without a decimal point, like 4195.
  2. Doubles − are floating-point numbers, like 3.14159 or 49.1.
  3. Booleans − have only two possible values either true or false.
  4. NULL − is a special type that only has one value: NULL.
  5. Strings − are sequences of characters, like 'PHP supports string operations.'
  6. Arrays − are named and indexed collections of other values.
  7. Objects − are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.
  8. Resources − are special variables that hold references to resources external to PHP (such as database connections).

The first five are simple types, and the next two (arrays and objects) are compound - the compound types can package up other arbitrary values of arbitrary type, whereas the simple types cannot.

We will explain only simple data type in this chapters. Array and Objects will be explained separately.

Integers

They are whole numbers, without a decimal point, like 4195. They are the simplest type .they correspond to simple whole numbers, both positive and negative. Integers can be assigned to variables, or they can be used in expressions, like so:

$int_var = 12345;
$another_int = -12345 + 12345;

Integer can be in decimal (base 10), octal (base 8), and hexadecimal (base 16) format. Decimal format is the default, octal integers are specified with a leading 0, and hexadecimals have a leading 0x.

For most common platforms, the largest integer is (2**31 . 1) (or 2,147,483,647), and the smallest (most negative) integer is . (2**31 . 1) (or .2,147,483,647).

Doubles

They like 3.14159 or 49.1. By default, doubles print with the minimum number of decimal places needed. For example, the code

<?php
   $many = 2.2888800;
   $many_2 = 2.2111200;
   $few = $many + $many_2;
   
   print("$many + $many_2 = $few 
"); ?>

It produces the following browser output:

2.28888 + 2.21112 = 4.5

Boolean

They have only two possible values either true or false. PHP provides a couple of constants especially for use as Booleans: TRUE and FALSE, which can be used like so

if (TRUE)
   print("This will always print
"); else print("This will never print<br>");

Interpreting other types as Booleans

Here are the rules for determine the "truth" of any value not already of the Boolean type:

  1. If the value is a number, it is false if exactly equal to zero and true otherwise.
  2. If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.
  3. Values of type NULL are always false.
  4. If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.
  5. Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).
  6. Don't use double as Booleans.

Each of the following variables has the truth value embedded in its name when it is used in a Boolean context.

$true_num = 3 + 0.14159;
$true_str = "Tried and true"
$true_array[49] = "An array element";
$false_array = array();
$false_null = NULL;
$false_num = 999 - 999;
$false_str = "";

NULL

NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this:

$my_var = NULL;

The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed

$my_var = null;

A variable that has been assigned NULL has the following properties:

  1. It evaluates to FALSE in a Boolean context.
  2. It returns FALSE when tested with IsSet() function.

Strings

They are sequences of characters, like "PHP supports string operations". Following are valid examples of string:

$string_1 = "This is a string in double quotes";
$string_2 = "This is a somewhat longer, singly quoted string";
$string_39 = "This string has thirty-nine characters";
$string_0 = ""; // a string with zero characters

Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values as well as specially interpreting certain character sequences.

<?php
   $variable = "name";
   $literally = 'My $variable will not print!';
   print($literally);
   print "<br>";
   
   $literally = "My $variable will print!";
   print($literally);
?>

This will produce following result:

My $variable will not print!\n
My name will print

There are no artificial limits on string length - within the bounds of available memory, you ought to be able to make arbitrarily long strings.

Strings that are delimited by double quotes (as in "this") are preprocessed in both the following two ways by PHP

  1. Certain character sequences beginning with backslash (\) are replaced with special characters
  2. Variable names (starting with $) are replaced with string representations of their values.

The escape-sequence replacements are:

  1. \n is replaced by the newline character
  2. \r is replaced by the carriage-return character
  3. \t is replaced by the tab character
  4. \$ is replaced by the dollar sign itself ($)
  5. \" is replaced by a single double-quote (")
  6. \\ is replaced by a single backslash (\)

Here Document

You can assign multiple lines to a single string variable using here document:

This will produce following result:

Variable Scope

Scope can be defined as the range of availability a variable has to the program in which it is declared. PHP variables can be one of four scope types:

  1. Local Variables: A variable declared in a function is considered local; that is, it can be referenced solely in that function. Any assignment outside of that function will be considered to be an entirely different variable from the one contained in the function.
    <?php
       $x = 4;
       
       function assignx () { 
          $x = 0;
          print "\$x inside function is $x. <br />";
       }
       
       assignx();
       print "\$x outside of function is $x. <br />";
    ?> 
    

    This will produce the following result:

    $x inside function is 0.
    $x outside of function is 4.
  2. Function Parameters: Function parameters are declared after the function name and inside parentheses. They are declared much like a typical variable would be:
    <?php
       // multiply a value by 10 and return it to the caller
       function multiply ($value) {
          $value = $value * 10;
          return $value;
       }
       
       $retval = multiply (10);
       Print "Return value is $retval\n";
    ?>
    

    This will produce the following result:

    Return value is 100 
  3. Global Variables: In contrast to local variables, a global variable can be accessed in any part of the program. However, in order to be modified, a global variable must be explicitly declared to be global in the function in which it is to be modified. This is accomplished, conveniently enough, by placing the keyword GLOBAL in front of the variable that should be recognized as global. Placing this keyword in front of an already existing variable tells PHP to use the variable having that name. Consider an example:
  4. <?php
       $somevar = 15;
       
       function addit() {
          GLOBAL $somevar;
          $somevar++;
          
          print "Somevar is $somevar";
       }
       
       addit();
    ?>
    

    This will produce the following result:

    Somevar is 16
  5. Static Variables: The final type of variable scoping that I discuss is known as static. In contrast to the variables declared as function parameters, which are destroyed on the function's exit, a static variable will not lose its value when the function exits and will still hold that value should the function be called again.
  6. You can declare a variable to be static simply by placing the keyword STATIC in front of the variable name.

    <?php
       function keep_track() {
          STATIC $count = 0;
          $count++;
          print $count;
          print "<br />";
       }
       
       keep_track();
       keep_track();
       keep_track();
    ?>
    

    This will produce the following result:

    1
    2
    3

Variable Naming

Rules for naming a variable is:

  1. Variable names must begin with a letter or underscore character.
  2. A variable name can consist of numbers, letters, underscores but you cannot use characters like + , - , % , ( , ) . & , etc

There is no size limit for variables.

A constant is a name or an identifier for a simple value. A constant value cannot change during the execution of the script. By default, a constant is case-sensitive. By convention, constant identifiers are always uppercase. A constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. If you have defined a constant, it can never be changed or undefined.

To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $. You can also use the function constant() to read a constant's value if you wish to obtain the constant's name dynamically.

constant() function

As indicated by the name, this function will return the value of the constant.

This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.

constant() example

<?php
   define("MINSIZE", 50);
   
   echo MINSIZE;
   echo constant("MINSIZE"); // same thing as the previous line
?>

Only scalar data (boolean, integer, float and string) can be contained in constants.

Differences between constants and variables are

  1. There is no need to write a dollar sign ($) before a constant, where as in Variable one has to write a dollar sign.
  2. Constants cannot be defined by simple assignment, they may only be defined using the define() function.
  3. Constants may be defined and accessed anywhere without regard to variable scoping rules.
  4. Once the Constants have been set, may not be redefined or undefined.

Valid and invalid constant names

// Valid constant names
define("ONE",     "first thing");
define("TWO2",    "second thing");
define("THREE_3", "third thing")

// Invalid constant names
define("2TWO",    "second thing");
define("__THREE__", "third value"); 

PHP Magic constants

PHP provides a large number of predefined constants to any script which it runs.

There are five magical constants that change depending on where they are used. For example, the value of __LINE__ depends on the line that it's used on in your script. These special constants are case-insensitive and are as follows:

Name Description
__LINE__ The current line number of the file.
__FILE__ The full path and filename of the file. If used inside an include,the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path whereas in older versions it contained relative path under some circumstances.
__FUNCTION__ The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__CLASS__ The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__METHOD__ The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).

What is Operator? Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. PHP language supports following type of operators.

  1. Arithmetic Operators
  2. Comparison Operators
  3. Logical (or Relational) Operators
  4. Assignment Operators
  5. Conditional (or ternary) Operators

Lets have a look on all operators one by one.

Arithmetic Operators

There are following arithmetic operators supported by PHP language.

Assume variable A holds 10 and variable B holds 20 then

Operator Description Example
+ Adds two operands A + B will give 30
- Subtracts second operand from the first A - B will give -10
* Multiply both operands A * B will give 200
/ Divide numerator by de-numerator. B / A will give 2
% Modulus Operator and remainder of after an integer division B % A will give 0
++ Increment operator, increases integer value by one A++ will give 11
-- Decrement operator, decreases integer value by one A-- will give 9

Comparison Operators

There are following comparison operators supported by PHP language.

Assume variable A holds 10 and variable B holds 20 then

Operator Description Example
== Checks if the value of two operands are equal or not, if yes then condition becomes true. (A == B) is not true.
!= Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true.
> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true.
< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true.
>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true.
<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.

Logical Operators

There are following logical operators supported by PHP language.

Assume variable A holds 10 and variable B holds 20 then

Operator Description Example
and Called Logical AND operator. If both the operands are true then condition becomes true. (A and B) is true.
or Called Logical OR Operator. If any of the two operands are non zero then condition becomes true. (A or B) is true.
&& Called Logical AND operator. If both the operands are non zero then condition becomes true. (A && B) is true.
|| Called Logical OR Operator. If any of the two operands are non zero then condition becomes true. (A || B) is true.
! Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false. !(A && B) is false.

Assignment Operators

There are following assignment operators supported by PHP language.

Operator Description Example
= Simple assignment operator, Assigns values from right side operands to left side operand C = A + B will assign value of A + B into C
+= Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand C += A is equivalent to C = C + A
-= Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand C -= A is equivalent to C = C - A
*= Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand C *= A is equivalent to C = C * A
/= Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand C /= A is equivalent to C = C / A
%= Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand C %= A is equivalent to C = C % A

Conditional Operator

There is one more operator called conditional operator. This first evaluates an expression for a true or false value and then execute one of the two given statements depending upon the result of the evaluation. The conditional operator has this syntax:

Operator Description Example
? : Conditional Expression If Condition is true ? Then value X : Otherwise value Y

Operators Categories

All the operators we have discussed above can be categorised into following categories:

  1. Unary prefix operators, which precede a single operand.
  2. Binary operators, which take two operands and perform a variety of arithmetic and logical operations.
  3. The conditional operator (a ternary operator), which takes three operands and evaluates either the second or third expression, depending on the evaluation of the first expression.
  4. Assignment operators, which assign a value to a variable.

Precedence of PHP Operators

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator

For example x = 7 + 3 * 2; Here x is assigned 13, not 20 because operator * has higher precedence than + so it first get multiplied with 3*2 and then adds into 7.

Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Category Operator Associativity
Unary ! ++ -- Right to left
Multiplicative * / % Left to right
Additive + - Left to right
Relational < <= > >= Left to right
Equality == != Left to right
Logical AND && Left to right
Logical OR || Left to right
Conditional ?: Right to left
Assignment = += -= *= /= %= Right to left

The if, elseif ...else and switch statements are used to take decision based on the different condition.

You can use conditional statements in your code to make your decisions. PHP supports following three decision making statements:

  1. if...else statement − use this statement if you want to execute a set of code when a condition is true and another if the condition is not true.
  2. elseif statement − is used with the if...else statement to execute a set of code if one of the several condition is true.
  3. switch statement − is used if you want to select one of many blocks of code to be executed, use the Switch statement. The switch statement is used to avoid long blocks of if..elseif..else code.

The If...Else Statement

If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.

Syntax

if (condition)
   code to be executed if condition is true;
else
   code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, Otherwise, it will output "Have a nice day!":

<html>
   <body>
   
      <?php
         $d=date("D");
         
         if ($d=="Fri")
            echo "Have a nice weekend!"; 
         
         else
            echo "Have a nice day!"; 
      ?>
   
   </body>
</html>

It will produce the following result:

Have a nice day!

The ElseIf Statement

If you want to execute some code if one of the several conditions are true use the elseif statement.

Syntax

if (condition)
   code to be executed if condition is true;
elseif (condition)
   code to be executed if condition is true;
else
   code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise, it will output "Have a nice day!"

<html>
   <body>
   
      <?php
         $d=date("D");
         
         if ($d=="Fri")
            echo "Have a nice weekend!";
         
         elseif ($d=="Sun")
            echo "Have a nice Sunday!"; 
         
         else
            echo "Have a nice day!"; 
      ?>
      
   </body>
</html>

It will produce the following result:

Have a nice day!

The Switch Statement

If you want to select one of many blocks of code to be executed, use the Switch statement.

The switch statement is used to avoid long blocks of if..elseif..else code.

Syntax

switch (expression)
{
   case label1:
      code to be executed if expression = label1;
      break;  
   
   case label2:
      code to be executed if expression = label2;
      break;
      default:
   
   code to be executed
   if expression is different 
   from both label1 and label2;
}

Example:

The switch statement works in an unusual way. First it evaluates given expression then seeks a lable to match the resulting value. If a matching value is found then the code associated with the matching label will be executed or if none of the lable matches then statement will execute any specified default code.

<html>
   <body>
      
      <?php
         $d=date("D");
         
         switch ($d)
         {
            case "Mon":
               echo "Today is Monday";
               break;
            
            case "Tue":
               echo "Today is Tuesday";
               break;
            
            case "Wed":
               echo "Today is Wednesday";
               break;
            
            case "Thu":
               echo "Today is Thursday";
               break;
            
            case "Fri":
               echo "Today is Friday";
               break;
            
            case "Sat":
               echo "Today is Saturday";
               break;
            
            case "Sun":
               echo "Today is Sunday";
               break;
            
            default:
               echo "Wonder which day is this ?";
         }

      ?>
   </body>
</html>

It will produce the following result:

Today is Wednesday

Loops in PHP are used to execute the same block of code a specified number of times. PHP supports following four loop types.

  1. for − loops through a block of code a specified number of times.
  2. while − loops through a block of code if and as long as a specified condition is true.
  3. do...while − loops through a block of code once, and then repeats the loop as long as a special condition is true.
  4. foreach − loops through a block of code for each element in an array.

We will discuss about continue and break keywords used to control the loops execution.

The for loop statement

The for statement is used when you know how many times you want to execute a statement or a block of statements.

Syntax

for (initialization; condition; increment)
{
   code to be executed;
}

The initializer is used to set the start value for the counter of the number of loop iterations. A variable may be declared here for this purpose and it is traditional to name it $i.

Example:

The following example makes five iterations and changes the assigned value of two variables on each pass of the loop.

<html>
   <body>
      
      <?php
         $a = 0;
         $b = 0;
         
         for( $i=0; $i<5; $i++ )
         {
            $a += 10;
            $b += 5;
         }
         
         echo ("At the end of the loop a=$a and b=$b" );
      ?>
	  
   </body>
</html>

This will produce the following result:

At the end of the loop a=50 and b=25

The while loop statement

The while statement will execute a block of code if and as long as a test expression is true.

If the test expression is true then the code block will be executed. After the code has executed the test expression will again be evaluated and the loop will continue until the test expression is found to be false.

Syntax

while (condition)
{
   code to be executed;
}

Example:

This example decrements a variable value on each iteration of the loop and the counter increments until it reaches 10 when the evaluation is false and the loop ends.

<html>
   <body>
   
      <?php
         $i = 0;
         $num = 50;
         
         while( $i < 10)
         {
            $num--;
            $i++;
         }
         
         echo ("Loop stopped at i = $i and num = $num" );
      ?>
      
   </body>
</html>

This will produce the following result:

Loop stopped at i = 10 and num = 40

The do...while loop statement

The do...while statement will execute a block of code at least once - it then will repeat the loop as long as a condition is true.

Syntax

do
{
   code to be executed;
}
while (condition);

The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 10

<html>
   <body>
   
      <?php
         $i = 0;
         $num = 0;
         
         do{
            $i++;
         }
         
         while( $i < 10 );
         echo ("Loop stopped at i = $i" );
      ?>
      
   </body>
</html>

This will produce the following result:

Loop stopped at i = 10

The foreach loop statement

The foreach statement is used to loop through arrays. For each pass the value of the current array element is assigned to $value and the array pointer is moved by one and in the next pass next element will be processed.

Syntax

foreach (array as value)
{
   code to be executed;

}

Example:

Try out following example to list out the values of an array.

<html>
   <body>
   
      <?php
         $array = array( 1, 2, 3, 4, 5);
         
         foreach( $array as $value )
         {
            echo "Value is $value <br />";
         }
      ?>
      
   </body>
</html>

This will produce the following result:

Value is 1
Value is 2
Value is 3
Value is 4
Value is 5

The break statement

The PHP break keyword is used to terminate the execution of a loop prematurely.

The break statement is situated inside the statement block. If gives you full control and whenever you want to exit from the loop you can come out. After coming out of a loop immediate statement to the loop will be executed.

Example:

In the following example condition test becomes true when the counter value reaches 3 and loop terminates.

<html>
   <body>
   
      <?php
         $i = 0;
         
         while( $i < 10)
         {
            $i++;
            if( $i == 3 )break;
         }
         echo ("Loop stopped at i = $i" );
      ?>
   
   </body>
</html>

This will produce the following result:

Loop stopped at i = 3

The continue statement

The PHP continue keyword is used to halt the current iteration of a loop but it does not terminate the loop.

Just like the break statement the continue statement is situated inside the statement block containing the code that the loop executes, preceded by a conditional test. For the pass encountering continue statement, rest of the loop code is skipped and next pass starts.

Example:

In the following example loop prints the value of array but for which condition becomes true it just skip the code and next value is printed.

<html>
   <body>
   
      <?php
         $array = array( 1, 2, 3, 4, 5);
         
         foreach( $array as $value )
         {
            if( $value == 3 )continue;
            echo "Value is $value <br />";
         }
      ?>
   
   </body>
</html>

This will produce the following result:

Value is 1
Value is 2
Value is 4
Value is 5

An array is a data structure that stores one or more similar type of values in a single value. For example if you want to store 100 numbers then instead of defining 100 variables its easy to define an array of 100 length.

There are three different kind of arrays and each array value is accessed using an ID c which is called array index.

  1. Numeric array − An array with a numeric index. Values are stored and accessed in linear fashion.
  2. Associative array − An array with strings as index. This stores element values in association with key values rather than in a strict linear index order.
  3. Multidimensional array − An array containing one or more arrays and values are accessed using multiple indices

Numeric Array

These arrays can store numbers, strings and any object but their index will be represented by numbers. By default array index starts from zero.

Example:

Following is the example showing how to create and access numeric arrays.

Here we have used array() function to create array. This function is explained in function reference.

<html>
   <body>
   
      <?php
         /* First method to create array. */
         $numbers = array( 1, 2, 3, 4, 5);
         
         foreach( $numbers as $value )
         {
            echo "Value is $value <br />";
         }
         
         /* Second method to create array. */
         $numbers[0] = "one";
         $numbers[1] = "two";
         $numbers[2] = "three";
         $numbers[3] = "four";
         $numbers[4] = "five";
         
         foreach( $numbers as $value )
         {
            echo "Value is $value <br />";
         }
      ?>
      
   </body>
</html>

This will produce the following result:

Value is 1
Value is 2
Value is 3
Value is 4
Value is 5
Value is one
Value is two
Value is three
Value is four
Value is five 

Associative Arrays

The associative arrays are very similar to numeric arrays in term of functionality but they are different in terms of their index. Associative array will have their index as string so that you can establish a strong association between key and values.

To store the salaries of employees in an array, a numerically indexed array would not be the best choice. Instead, we could use the employees names as the keys in our associative array, and the value would be their respective salary.

NOTE − Don't keep associative array inside double quote while printing otherwise it would not return any value.

Example:

<html>
   <body>
      
      <?php
         /* First method to associate create array. */
         $salaries = array("mohammad" => 2000, "qadir" => 1000, "zara" => 500);
         
         echo "Salary of mohammad is ". $salaries['mohammad'] . "<br />";
         echo "Salary of qadir is ".  $salaries['qadir']. "<br />";
         echo "Salary of zara is ".  $salaries['zara']. "<br />";
         
         /* Second method to create array. */
         $salaries['mohammad'] = "high";
         $salaries['qadir'] = "medium";
         $salaries['zara'] = "low";
         
         echo "Salary of mohammad is ". $salaries['mohammad'] . "<br />";
         echo "Salary of qadir is ".  $salaries['qadir']. "<br />";
         echo "Salary of zara is ".  $salaries['zara']. "<br />";
      ?>
   
   </body>
</html>

This will produce the following result:

Salary of mohammad is 2000
Salary of qadir is 1000
Salary of zara is 500
Salary of mohammad is high
Salary of qadir is medium
Salary of zara is low

Multidimensional Arrays

A multi-dimensional array each element in the main array can also be an array. And each element in the sub-array can be an array, and so on. Values in the multi-dimensional array are accessed using multiple index.

Example:

In this example we create a two dimensional array to store marks of three students in three subjects

This example is an associative array, you can create numeric array in the same fashion.

<html>
   <body>
      
      <?php
         $marks = array( 
            "mohammad" => array
            (
               "physics" => 35,
               "maths" => 30,	
               "chemistry" => 39
            ),
            
            "qadir" => array
            (
               "physics" => 30,
               "maths" => 32,
               "chemistry" => 29
            ),
            
            "zara" => array
            (
               "physics" => 31,
               "maths" => 22,
               "chemistry" => 39
            )
         );
         
         /* Accessing multi-dimensional array values */
         echo "Marks for mohammad in physics : " ;
         echo $marks['mohammad']['physics'] . "<br />"; 
         
         echo "Marks for qadir in maths : ";
         echo $marks['qadir']['maths'] . "<br />"; 
         
         echo "Marks for zara in chemistry : " ;
         echo $marks['zara']['chemistry'] . "<br />"; 
      ?>
   
   </body>
</html>

This will produce the following result:

Marks for mohammad in physics : 35
Marks for qadir in maths : 32
Marks for zara in chemistry : 39

They are sequences of characters, like "PHP supports string operations".

Following are valid examples of string

$string_1 = "This is a string in double quotes";
$string_2 = "This is a somewhat longer, singly quoted string";
$string_39 = "This string has thirty-nine characters";
$string_0 = ""; // a string with zero characters

Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values as well as specially interpreting certain character sequences.

<?php
   $variable = "name";
   $literally = 'My $variable will not print!\\n';
   
   print($literally);
   print "<br />";
   
   $literally = "My $variable will print!\\n";
   
   print($literally);
?>

This will produce the following result

My $variable will not print!\n
My name will print

There are no artificial limits on string length - within the bounds of available memory, you ought to be able to make arbitrarily long strings.

Strings that are delimited by double quotes (as in "this") are preprocessed in both the following two ways by PHP:

  1. Certain character sequences beginning with backslash (\) are replaced with special characters
  2. Variable names (starting with $) are replaced with string representations of their values.

The escape-sequence replacements are:

  1. \n is replaced by the newline character
  2. \r is replaced by the carriage-return character
  3. \t is replaced by the tab character
  4. \$ is replaced by the dollar sign itself ($)
  5. \" is replaced by a single double-quote (")
  6. \\ is replaced by a single backslash (\)

String Concatenation Operator

To concatenate two string variables together, use the dot (.) operator:

<?php
   $string1="Hello World";
   $string2="1234";
   
   echo $string1 . " " . $string2;
?>

This will produce the following result:

Hello World 1234

If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string.

Between the two string variables we added a string with a single character, an empty space, to separate the two variables.

Using the strlen() function

The strlen() function is used to find the length of a string.

Let's find the length of our string "Hello world!":

<?php
   echo strlen("Hello world!");
?>

This will produce the following result:

12

The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string)

Using the strpos() function

The strpos() function is used to search for a string or character within a string.

If a match is found in the string, this function will return the position of the first match. If no match is found, it will return FALSE.

Let's see if we can find the string "world" in our string:

<?php
   echo strpos("Hello world!","world");
?>

This will produce the following result:

6

As you see the position of the string "world" in our string is position 6. The reason that it is 6, and not 7, is that the first position in the string is 0, and not 1.

This session demonstrates how PHP can provide dynamic content according to browser type, randomly generated numbers or User Input. It also demonstrated how the client browser can be redirected.

Identifying Browser & Platform

PHP creates some useful environment variables that can be seen in the phpinfo.php page that was used to setup the PHP environment.

One of the environment variables set by PHP is HTTP_USER_AGENT which identifies the user's browser and operating system.

PHP provides a function getenv() to access the value of all the environment variables. The information contained in the HTTP_USER_AGENT environment variable can be used to create dynamic content appropriate to the browser.

Following example demonstrates how you can identify a client browser and operating system

NOTE: The function preg_match()is discussed in PHP Regular expression session.

<html>
   <body>
   
      <?php
         function getBrowser()
         { 
            $u_agent = $_SERVER['HTTP_USER_AGENT']; 
            $bname = 'Unknown';
            $platform = 'Unknown';
            $version= "";
            
            //First get the platform?
            if (preg_match('/linux/i', $u_agent)) {
               $platform = 'linux';
            }
            
            elseif (preg_match('/macintosh|mac os x/i', $u_agent)) {
               $platform = 'mac';
            }
            
            elseif (preg_match('/windows|win32/i', $u_agent)) {
               $platform = 'windows';
            }
            
            // Next get the name of the useragent yes seperately and for good reason
            if(preg_match('/MSIE/i',$u_agent) && !preg_match('/Opera/i',$u_agent))
            {
               $bname = 'Internet Explorer';
               $ub = "MSIE";
            }
            
            elseif(preg_match('/Firefox/i',$u_agent))
            {
               $bname = 'Mozilla Firefox';
               $ub = "Firefox";
            }
            
            elseif(preg_match('/Chrome/i',$u_agent))
            {
               $bname = 'Google Chrome';
               $ub = "Chrome";
            }
            
            elseif(preg_match('/Safari/i',$u_agent))
            {
               $bname = 'Apple Safari';
               $ub = "Safari";
            }
            
            elseif(preg_match('/Opera/i',$u_agent))
            {
               $bname = 'Opera';
               $ub = "Opera";
            }
            
            elseif(preg_match('/Netscape/i',$u_agent))
            {
               $bname = 'Netscape';
               $ub = "Netscape";
            }
            
            // finally get the correct version number
            $known = array('Version', $ub, 'other');
            $pattern = '#(?' . join('|', $known) . ')[/ ]+(?<version>[0-9.|a-zA-Z.]*)#';
            
            if (!preg_match_all($pattern, $u_agent, $matches)) {
               // we have no matching number just continue
            }
            
            // see how many we have
            $i = count($matches['browser']);
            
            if ($i != 1) {
               //we will have two since we are not using 'other' argument yet
               
               //see if version is before or after the name
               if (strripos($u_agent,"Version") < strripos($u_agent,$ub)){
                  $version= $matches['version'][0];
               }
               else {
                  $version= $matches['version'][1];
               }
            }
            else {
               $version= $matches['version'][0];
            }
            
            // check if we have a number
            if ($version==null || $version=="") {$version="?";}
            return array(
               'userAgent' => $u_agent,
               'name'      => $bname,
               'version'   => $version,
               'platform'  => $platform,
               'pattern'   => $pattern
            );
         }
         
         // now try it
         $ua=getBrowser();
         $yourbrowser= "Your browser: " . $ua['name'] . " " . $ua['version'] . " on " .$ua['platform'] . " reports: <br >" . $ua['userAgent'];
         
         print_r($yourbrowser);
      ?>
   
   </body>
</html>

This is producing following result on my machine. This result may be different for your computer depending on what you are using.

It will produce the following result:

Your browser: Mozilla Firefox 40.0 on windows reports:
Mozilla/5.0 (Windows NT 6.1; rv:40.0) Gecko/20100101 Firefox/40.0 

Display Images Randomly

The PHP rand() function is used to generate a random number.i This function can generate numbers with-in a given range. The random number generator should be seeded to prevent a regular pattern of numbers being generated. This is achieved using the srand() function that specifies the seed number as its argument.

Following example demonstrates how you can display different image each time out of four images

<html>
   <body>
   
      <?php
         srand( microtime() * 1000000 );
         $num = rand( 1, 4 );
         
         switch( $num )
         {
            case 1: $image_file = "/php/images/logo.png";
               break;
            
            case 2: $image_file = "/php/images/php.jpg";
               break;
            
            case 3: $image_file = "/php/images/logo.png";
               break;
            
            case 4: $image_file = "/php/images/php.jpg";
               break;
         }
         echo "Random Image : <img src=$image_file />";
      ?>
      
   </body>
</html>

Using HTML Forms

The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.

Try out following example by putting the source code in test.php script.

<?php
   if( $_POST["name"] || $_POST["age"] )
   {
      if (preg_match("/[^A-Za-z'-]/",$_POST['name'] ))
      {
         die ("invalid name and name should be alpha");
      }
      
      echo "Welcome ". $_POST['name']. "<br />";
      echo "You are ". $_POST['age']. " years old.";
      
      exit();
   }
?>
<html>
   <body>
   
      <form action="<?php $_PHP_SELF ?>" method="POST">
         Name: <input type="text" name="name" />
         Age: <input type="text" name="age" />
         <input type="submit" />
      </form>
      
   </body>
</html>

It will produce the following result:

  1. The PHP default variable $_PHP_SELF is used for the PHP script name and when you click "submit" button then same PHP script will be called and will produce following result
  2. The method = "POST" is used to post user data to the server script. There are two methods of posting data to the server script which are discussed in PHP GET & POST chapter.

Browser Redirection

The PHP header() function supplies raw HTTP headers to the browser and can be used to redirect it to another location. The redirection script should be at the very top of the page to prevent any other part of the page from loading.

The target is specified by the Location: header as the argument to the header() function. After calling this function the exit() function can be used to halt parsing of rest of the code.

Following example demonstrates how you can redirect a browser request to another web page. Try out this example by putting the source code in test.php script.

<?php
   if( $_POST["location"] )
   {
      $location = $_POST["location"];
      header( "Location:$location" );
      
      exit();
   }
?>
<html>
   <body>
   
      <p>Choose a site to visit :</p>
      
      <form action="<?php $_SERVER['PHP_SELF'] ?>" method="POST">
         <select name="location">.
         
            <option value="http://www.isolutionsynergyideas.com">
               iSolutionSynergyIdeas.com
            </option>
         
            <option value="http://www.google.com">
               Google Search Page
            </option>
         
         </select>
         <input type="submit" />
      </form>
      
   </body>
</html>

It will produce the following result:

Displaying "File Download" Dialog Box

Sometime it is desired that you want to give option where a use will click a link and it will pop up a "File Download" box to the user in stead of displaying actual content. This is very easy and will be achieved through HTTP header.

The HTTP header will be different from the actual header where we send Content-Type as text/html\n\n. In this case content type will be application/octet-stream and actual file name will be concatenated along with it.

For example,if you want make a FileName file downloadable from a given link then its syntax will be as follows.

#!/usr/bin/perl

# HTTP Header
print "Content-Type:application/octet-stream; name=\"FileName\"\r\n";
print "Content-Disposition: attachment; filename=\"FileName\"\r\n\n";

# Actual File Content
open( FILE, "		
                                

There are two ways the browser client can send information to the web server.

  1. The GET Method
  2. The POST Method

Before the browser sends the information, it encodes it using a scheme called URL encoding. In this scheme, name/value pairs are joined with equal signs and different pairs are separated by the ampersand.

name1=value1&name2=value2&name3=value3

Spaces are removed and replaced with the + character and any other nonalphanumeric characters are replaced with a hexadecimal values. After the information is encoded it is sent to the server.

The GET Method

The GET method sends the encoded user information appended to the page request. The page and the encoded information are separated by the ? character.

http://www.test.com/index.htm?name1=value1&name2=value2
  1. The GET method produces a long string that appears in your server logs, in the browser's Location: box.
  2. The GET method is restricted to send upto 1024 characters only.
  3. Never use GET method if you have password or other sensitive information to be sent to the server.
  4. GET can't be used to send binary data, like images or word documents, to the server.
  5. The data sent by GET method can be accessed using QUERY_STRING environment variable.
  6. The PHP provides $_GET associative array to access all the sent information using GET method.

Try out following example by putting the source code in test.php script.

<?php
   if( $_GET["name"] || $_GET["age"] )
   {
      echo "Welcome ". $_GET['name']. "<br />";
      echo "You are ". $_GET['age']. " years old.";
      
      exit();
   }
?>
<html>
   <body>
   
      <form action="<?php $_PHP_SELF ?>" method="GET">
         Name: <input type="text" name="name" />
         Age: <input type="text" name="age" />
         <input type="submit" />
      </form>
      
   </body>
</html>

It will produce the following result:

The POST Method

The POST method transfers information via HTTP headers. The information is encoded as described in case of GET method and put into a header called QUERY_STRING.

  1. The POST method does not have any restriction on data size to be sent.
  2. The POST method can be used to send ASCII as well as binary data.
  3. The data sent by POST method goes through HTTP header so security depends on HTTP protocol. By using Secure HTTP you can make sure that your information is secure.
  4. The PHP provides $_POST associative array to access all the sent information using POST method.

Try out following example by putting the source code in test.php script.

<?php
   if( $_POST["name"] || $_POST["age"] )
   {
      if (preg_match("/[^A-Za-z'-]/",$_POST['name'] ))
      {
         die ("invalid name and name should be alpha");
		}
      echo "Welcome ". $_POST['name']. "<br />";
      echo "You are ". $_POST['age']. " years old.";
      
      exit();
   }
?>
<html>
   <body>
   
      <form action="<?php $_PHP_SELF ?>" method="POST">
         Name: <input type="text" name="name" />
         Age: <input type="text" name="age" />
         <input type="submit" />
      </form>
   
   </body>
</html>

It will produce the following result:

The $_REQUEST variable

The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE. We will discuss $_COOKIE variable when we will explain about cookies.

The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.

Try out following example by putting the source code in test.php script.

<?php
   if( $_REQUEST["name"] || $_REQUEST["age"] )
   {
      echo "Welcome ". $_REQUEST['name']. "<br />";
      echo "You are ". $_REQUEST['age']. " years old.";
      exit();
   }
?>
<html>
   <body>
      
      <form action="<?php $_PHP_SELF ?>" method="POST">
         Name: <input type="text" name="name" />
         Age: <input type="text" name="age" />
         <input type="submit" />
      </form>
      
   </body>
</html>

Here $_PHP_SELF variable contains the name of self script in which it is being called.

It will produce the following result:

You can include the content of a PHP file into another PHP file before the server executes it. There are two PHP functions which can be used to included one PHP file into another PHP file.

  1. The include() Function
  2. The require() Function

This is a strong point of PHP which helps in creating functions, headers, footers, or elements that can be reused on multiple pages. This will help developers to make it easy to change the layout of complete website with minimal effort. If there is any change required then instead of changing thousand of files just change included file.

The include() Function

The include() function takes all the text in a specified file and copies it into the file that uses the include function. If there is any problem in loading a file then the include() function generates a warning but the script will continue execution.

Assume you want to create a common menu for your website. Then create a file menu.php with the following content.

<a href="http://www.isolutionsynergyideas.com/home">Home</a> - 
<a href="http://www.isolutionsynergyideas.com/html">HTML</a> - 
<a href="http://www.isolutionsynergyideas.com/php">PHP</a> - 
<a href="http://www.isolutionsynergyideas.com/socialMedia">Social Media</a> <br />

Now create as many pages as you like and include this file to create header. For example now your test.php file can have following content.

<html>
   <body>
   
      <?php include("menu.php"); ?>
      <p>This is an example to show how to include PHP file!</p>
      
   </body>
</html>

It will produce the following result:

Home - 
HTML - 
PHP - 
Social Media 

This is an example to show how to include PHP file!

The require() Function

The require() function takes all the text in a specified file and copies it into the file that uses the include function. If there is any problem in loading a file then the require() function generates a fatal error and halt the execution of the script.

So there is no difference in require() and include() except they handle error conditions. It is recommended to use the require() function instead of include(), because scripts should not continue executing if files are missing or misnamed.

You can try using above example with require() function and it will generate same result. But if you will try following two examples where file does not exist then you will get different results.

<html>
   <body>
   
      <?php include("xxmenu.php"); ?>
      <p>This is an example to show how to include wrong PHP file!</p>
      
   </body>
/html>

This will produce the following result:

This is an example to show how to include wrong PHP file!

Now lets try same example with require() function.

<html>
   <body>
   
      <?php require("xxmenu.php"); ?>
      <p>This is an example to show how to include wrong PHP file!</p>
      
   </body>
/html>

This time file execution halts and nothing is displayed.

NOTE − You may get plain warning messages or fatal error messages or nothing at all. This depends on your PHP Server configuration.

This chapter will explain following functions related to files:

  1. Opening a file
  2. Reading a file
  3. Writing a file
  4. Closing a file

Opening and Closing Files

The PHP fopen() function is used to open a file. It requires two arguments stating first the file name and then mode in which to operate.

Files modes can be specified as one of the six options in this table.

Mode Purpose
r Opens the file for reading only.
Places the file pointer at the beginning of the file.
r+ Opens the file for reading and writing.
Places the file pointer at the beginning of the file.
w Opens the file for writing only.
Places the file pointer at the beginning of the file.
and truncates the file to zero length. If files does not exist then it attempts to create a file.
w+ Opens the file for reading and writing only.
Places the file pointer at the beginning of the file.
and truncates the file to zero length. If files does not exist then it attempts to create a file.
a Opens the file for writing only.
Places the file pointer at the end of the file.
and If files does not exist then it attempts to create a file.
a+ Opens the file for reading and writing only.
Places the file pointer at the end of the file.
and If files does not exist then it attempts to create a file.

If an attempt to open a file fails then fopen returns a value of false otherwise it returns a file pointer which is used for further reading or writing to that file.

After making a changes to the opened file it is important to close it with the fclose() function. The fclose() function requires a file pointer as its argument and then returns true when the closure succeeds or false if it fails.

Reading a file

Once a file is opened using fopen() function it can be read with a function called fread(). This function requires two arguments. These must be the file pointer and the length of the file expressed in bytes.

The files length can be found using the filesize() function which takes the file name as its argument and returns the size of the file expressed in bytes.

So here are the steps required to read a file with PHP.

  1. Open a file using fopen() function.
  2. Get the file's length using filesize() function.
  3. Read the file's content using fread() function.
  4. Close the file with fclose() function.

The following example assigns the content of a text file to a variable then displays those contents on the web page.

<html>

   <head>
      <title>Reading a file using PHP</title>
   </head>
   
   <body>
      
      <?php
         $filename = "tmp.txt";
         $file = fopen( $filename, "r" );
         
         if( $file == false )
         {
            echo ( "Error in opening file" );
            exit();
         }
         
         $filesize = filesize( $filename );
         $filetext = fread( $file, $filesize );
         fclose( $file );
         
         echo ( "File size : $filesize bytes" );
         echo ( "<pre>$filetext</pre>" );
      ?>
      
   </body>
</html>

It will produce the following result:

File size : 278 bytes

The PHP Hypertext Preprocessor (PHP) is a programming 
language that allows web developers to create dynamic 
content that interacts with databases.
PHP is basically used for developing web based software 
applications. This tutorial helps you to build your base
 with PHP.

Writing a file

A new file can be written or text can be appended to an existing file using the PHP fwrite() function. This function requires two arguments specifying a file pointer and the string of data that is to be written. Optionally a third integer argument can be included to specify the length of the data to write. If the third argument is included, writing would will stop after the specified length has been reached.

The following example creates a new text file then writes a short text heading inside it. After closing this file its existence is confirmed using file_exist() function which takes file name as an argument

<?php
   $filename = "/home/user/guest/newfile.txt";
   $file = fopen( $filename, "w" );
   
   if( $file == false )
   {
      echo ( "Error in opening new file" );
      exit();
   }
   fwrite( $file, "This is  a simple test\n" );
   fclose( $file );
?>
<html>
   
   <head>
      <title>Writing a file using PHP</title>
   </head>
   
   <body>
      
      <?php
         $filename = "newfile.txt";
         $file = fopen( $filename, "r" );
         
         if( $file == false )
         {
            echo ( "Error in opening file" );
            exit();
         }
         
         $filesize = filesize( $filename );
         $filetext = fread( $file, $filesize );
         
         fclose( $file );
         
         echo ( "File size : $filesize bytes" );
         echo ( "$filetext" );
         echo("file name: $filename");
      ?>
      
   </body>
</html>

It will produce the following result:

Error in opening new file

PHP functions are similar to other programming languages. A function is a piece of code which takes one more input in the form of parameter and does some processing and returns a value.

You already have seen many functions like fopen() and fread() etc. They are built-in functions but PHP gives you option to create your own functions as well.

There are two parts which should be clear to you:

  1. Creating a PHP Function
  2. Calling a PHP Function

In fact you hardly need to create your own PHP function because there are already more than 1000 of built-in library functions created for different area and you just need to call them according to your requirement.

Creating PHP Function

Its very easy to create your own PHP function. Suppose you want to create a PHP function which will simply write a simple message on your browser when you will call it. Following example creates a function called writeMessage() and then calls it just after creating it.

Note that while creating a function its name should start with keyword function and all the PHP code should be put inside { and } braces as shown in the following example below:

<html>
   
   <head>
      <title>Writing PHP Function</title>
   </head>
   
   <body>
      
      <?php
         /* Defining a PHP Function */
         function writeMessage()
         {
            echo "You are really a nice person, Have a nice time!";
         }
         
         /* Calling a PHP Function */
         writeMessage();
      ?>
      
   </body>
</html>

This will display following result:

You are really a nice person, Have a nice time!

PHP Functions with Parameters

PHP gives you option to pass your parameters inside a function. You can pass as many as parameters your like. These parameters work like variables inside your function. Following example takes two integer parameters and add them together and then print them.

<html>
   
   <head>
      <title>Writing PHP Function with Parameters</title>
   </head>
   
   <body>
   
      <?php
         function addFunction($num1, $num2)
         {
            $sum = $num1 + $num2;
            echo "Sum of the two numbers is : $sum";
         }
         
         addFunction(10, 20);
      ?>
      
   </body>
</html>

This will display following result:

Sum of the two numbers is : 30

Passing Arguments by Reference

It is possible to pass arguments to functions by reference. This means that a reference to the variable is manipulated by the function rather than a copy of the variable's value.

Any changes made to an argument in these cases will change the value of the original variable. You can pass an argument by reference by adding an ampersand to the variable name in either the function call or the function definition.

Following example depicts both the cases.

<html>
   
   <head>
      <title>Passing Argument by Reference</title>
   </head>
   
   <body>
      
      <?php
         function addFive($num)
         {
            $num += 5;
         }
         
         function addSix(&$num)
         {
            $num += 6;
         }
         $orignum = 10;
         addFive( $orignum );
         
         echo "Original Value is $orignum<br />";
         
         addSix( $orignum );
         echo "Original Value is $orignum<br />";
      ?>
      
   </body>
</html>

This will display following result:

Original Value is 10
Original Value is 16 

PHP Functions returning value

A function can return a value using the return statement in conjunction with a value or object. return stops the execution of the function and sends the value back to the calling code.

You can return more than one value from a function using return array(1,2,3,4).

Following example takes two integer parameters and add them together and then returns their sum to the calling program. Note that return keyword is used to return a value from a function.

<html>
   
   <head>
      <title>Writing PHP Function which returns value</title>
   </head>
   
   <body>
   
      <?php
         function addFunction($num1, $num2)
         {
            $sum = $num1 + $num2;
            return $sum;
         }
         $return_value = addFunction(10, 20);
         
         echo "Returned value from the function : $return_value";
      ?>
      
   </body>
</html>

This will display following result:

Returned value from the function: 30

Setting Default Values for Function Parameters

You can set a parameter to have a default value if the function's caller doesn't pass it.

Following function prints NULL in case use does not pass any value to this function.

<html>
   
   <head>
      <title>Writing PHP Function which returns value</title>
   </head>
   
   <body>
      
      <?php
         function printMe($param = NULL)
         {
            print $param;
         }
         printMe("This is test");
         printMe();
      ?>
      
   </body>
</html>

This will produce following result:

This is test

Dynamic Function Calls

It is possible to assign function names as strings to variables and then treat these variables exactly as you would the function name itself. Following example depicts this behaviour.

<html>
   
   <head>
      <title>Dynamic Function Calls</title>
   </head>
   
   <body>
      
      <?php
         function sayHello()
         {
            echo "Hello<br />";
         }
         $function_holder = "sayHello";
         $function_holder();
      ?>
      
   </body>
</html>

This will display following result

Hello

Cookies are text files stored on the client computer and they are kept of use tracking purpose. PHP transparently supports HTTP cookies.

There are three steps involved in identifying returning users:

  1. Server script sends a set of cookies to the browser. For example name, age, or identification number etc.
  2. Browser stores this information on local machine for future use.
  3. When next time browser sends any request to web server then it sends those cookies information to the server and server uses that information to identify the user.

This chapter will teach you how to set cookies, how to access them and how to delete them.

The Anatomy of a Cookie

Cookies are usually set in an HTTP header (although JavaScript can also set a cookie directly on a browser). A PHP script that sets a cookie might send headers that look something like this:

HTTP/1.1 200 OK
Date: Fri, 04 Feb 2000 21:03:38 GMT
Server: Apache/1.3.9 (UNIX) PHP/4.0b3
Set-Cookie: name=xyz; expires=Friday, 04-Feb-07 22:03:38 GMT; 
                 path=/; domain=isolutionsynergyideas.com
Connection: close
Content-Type: text/html

As you can see, the Set-Cookie header contains a name value pair, a GMT date, a path and a domain. The name and value will be URL encoded. The expires field is an instruction to the browser to "forget" the cookie after the given time and date.

If the browser is configured to store cookies, it will then keep this information until the expiry date. If the user points the browser at any page that matches the path and domain of the cookie, it will resend the cookie to the server.The browser's headers might look something like this

GET / HTTP/1.0
Connection: Keep-Alive
User-Agent: Mozilla/4.6 (X11; I; Linux 2.2.6-15apmac ppc)
Host: zink.demon.co.uk:1126
Accept: image/gif, */*
Accept-Encoding: gzip
Accept-Language: en
Accept-Charset: iso-8859-1,*,utf-8
Cookie: name=xyz

A PHP script will then have access to the cookie in the environmental variables $_COOKIE or $HTTP_COOKIE_VARS[] which holds all cookie names and values. Above cookie can be accessed using $HTTP_COOKIE_VARS["name"].

Setting Cookies with PHP

PHP provided setcookie() function to set a cookie. This function requires upto six arguments and should be called before <html> tag. For each cookie this function has to be called separately.

setcookie(name, value, expire, path, domain, security);

Here is the detail of all the arguments:

  1. Name: This sets the name of the cookie and is stored in an environment variable called HTTP_COOKIE_VARS. This variable is used while accessing cookies.
  2. Value: This sets the value of the named variable and is the content that you actually want to store.
  3. Expiry: This specify a future time in seconds since 00:00:00 GMT on 1st Jan 1970. After this time cookie will become inaccessible. If this parameter is not set then cookie will automatically expire when the Web Browser is closed.
  4. Path: This specifies the directories for which the cookie is valid. A single forward slash character permits the cookie to be valid for all directories.
  5. Domain: This can be used to specify the domain name in very large domains and must contain at least two periods to be valid. All cookies are only valid for the host and domain which created them.
  6. Security: This can be set to 1 to specify that the cookie should only be sent by secure transmission using HTTPS otherwise set to 0 which mean cookie can be sent by regular HTTP.

Following example will create two cookies name and age these cookies will be expired after one hour.

<?php
   setcookie("name", "John Watkin", time()+3600, "/","", 0);
   setcookie("age", "36", time()+3600, "/", "",  0);
?>
<html>
   
   <head>
      <title>Setting Cookies with PHP</title>
   </head>
   
   <body>
      <?php echo "Set Cookies"?>
   </body>
   
</html>

Accessing Cookies with PHP

PHP provides many ways to access cookies. Simplest way is to use either $_COOKIE or $HTTP_COOKIE_VARS variables. Following example will access all the cookies set in above example.

<html>
   
   <head>
      <title>Accessing Cookies with PHP</title>
   </head>
   
   <body>
      
      <?php
         echo $_COOKIE["name"]. "<br />";
         
         /* is equivalent to */
         echo $HTTP_COOKIE_VARS["name"]. "<br />";
         
         echo $_COOKIE["age"] . "<br />";
         
         /* is equivalent to */
         echo $HTTP_COOKIE_VARS["name"] . "<br />";
      ?>
      
   </body>
</html>

You can use isset() function to check if a cookie is set or not.

<html>
   
   <head>
      <title>Accessing Cookies with PHP</title>
   </head>
   
   <body>
      
      <?php
         if( isset($_COOKIE["name"]))
            echo "Welcome " . $_COOKIE["name"] . "<br />";
         
         else
            echo "Sorry... Not recognized" . "<br />";
      ?>
      
   </body>
</html>

Deleting Cookie with PHP

Officially, to delete a cookie you should call setcookie() with the name argument only but this does not always work well, however, and should not be relied on.

It is safest to set the cookie with a date that has already expired.

<?php
   setcookie( "name", "", time()- 60, "/","", 0);
   setcookie( "age", "", time()- 60, "/","", 0);
?>
<html>
   
   <head>
      <title>Deleting Cookies with PHP</title>
   </head>
   
   <body>
      <?php echo "Deleted Cookies" ?>
   </body>
   
</html>

An alternative way to make data accessible across the various pages of an entire website is to use a PHP Session.

A session creates a file in a temporary directory on the server where registered session variables and their values are stored. This data will be available to all pages on the site during that visit.

The location of the temporary file is determined by a setting in the php.ini file called session.save_path. Bore using any session variable make sure you have setup this path.

When a session is started following things happen:

  1. PHP first creates a unique identifier for that particular session which is a random string of 32 hexadecimal numbers such as 3c7foj34c3jj973hjkop2fc937e3443.
  2. A cookie called PHPSESSID is automatically sent to the user's computer to store unique session identification string.
  3. A file is automatically created on the server in the designated temporary directory and bears the name of the unique identifier prefixed by sess_ ie sess_3c7foj34c3jj973hjkop2fc937e3443.

When a PHP script wants to retrieve the value from a session variable, PHP automatically gets the unique session identifier string from the PHPSESSID cookie and then looks in its temporary directory for the file bearing that name and a validation can be done by comparing both values.

A session ends when the user loses the browser or after leaving the site, the server will terminate the session after a predetermined period of time, commonly 30 minutes duration.

Starting a PHP Session

A PHP session is easily started by making a call to the session_start() function.This function first checks if a session is already started and if none is started then it starts one. It is recommended to put the call to session_start() at the beginning of the page.

Session variables are stored in associative array called $_SESSION[]. These variables can be accessed during lifetime of a session.

The following example starts a session then register a variable called counter that is incremented each time the page is visited during the session.

Make use of isset() function to check if session variable is already set or not.

Put this code in a test.php file and load this file many times to see the result.

<?php
   session_start();
   
   if( isset( $_SESSION['counter'] ) )
   {
      $_SESSION['counter'] += 1;
   }
   else
   {
      $_SESSION['counter'] = 1;
   }
   $msg = "You have visited this page ".  $_SESSION['counter'];
   $msg .= "in this session.";
?>
<html>
   
   <head>
      <title>Setting up a PHP session</title>
   </head>
   
   <body>
      <?php  echo ( $msg ); ?>
   </body>
   
</html>

It will produce the following result:

You have visited this page 1in this session.

Destroying a PHP Session

A PHP session can be destroyed by session_destroy() function. This function does not need any argument and a single call can destroy all the session variables. If you want to destroy a single session variable then you can use unset() function to unset a session variable.

Here is the example to unset a single variable:

<?php
   unset($_SESSION['counter']);
?>

Here is the call which will destroy all the session variables:

<?php
   session_destroy();
?>

Turning on Auto Session

You don't need to call start_session() function to start a session when a user visits your site if you can set session.auto_start variable to 1 in php.ini file.

Sessions without cookies

There may be a case when a user does not allow to store cookies on their machine. So there is another method to send session ID to the browser.

Alternatively, you can use the constant SID which is defined if the session started. If the client did not send an appropriate session cookie, it has the form session_name=session_id. Otherwise, it expands to an empty string. Thus, you can embed it unconditionally into URLs.

The following example demonstrates how to register a variable, and how to link correctly to another page using SID.

<?php
   session_start();
   
   if (isset($_SESSION['counter'])) {
      $_SESSION['counter'] = 1;
   }
   else {
      $_SESSION['counter']++;
   }
   
   $msg = "You have visited this page ".  $_SESSION['counter'];
   $msg .= "in this session.";
   
   echo ( $msg );
?>
<p>
   To continue  click following link <br />
   
   <a  href="nextpage.php?<?php echo htmlspecialchars(SID); ?>">
</p>

It will produce the following result:

You have visited this page 1in this session.

To continue click following link 

The htmlspecialchars() may be used when printing the SID in order to prevent XSS related attacks.

PHP must be configured correctly in the php.ini file with the details of how your system sends email. Open php.ini file available in /etc/ directory and find the section headed [mail function].

Windows users should ensure that two directives are supplied. The first is called SMTP that defines your email server address. The second is called sendmail_from which defines your own email address.

The configuration for Windows should look something like this:

[mail function]
; For Win32 only.
SMTP = smtp.secureserver.net

; For win32 only
sendmail_from = info@isolutionsynergyideas.com

Linux users simply need to let PHP know the location of their sendmail application. The path and any desired switches should be specified to the sendmail_path directive.

The configuration for Linux should look something like this:

[mail function]
; For Win32 only.
SMTP = 

; For win32 only
sendmail_from = 

; For Unix only
sendmail_path = /usr/sbin/sendmail -t -i

Now you are ready to go

Sending plain text email

PHP makes use of mail() function to send an email. This function requires three mandatory arguments that specify the recipient's email address, the subject of the the message and the actual message additionally there are other two optional parameters.

mail( to, subject, message, headers, parameters );

Here is the description for each parameters.

Parameter Description
to Required. Specifies the receiver / receivers of the email
subject Required. Specifies the subject of the email. This parameter cannot contain any newline characters
message Required. Defines the message to be sent. Each line should be separated with a LF (\n). Lines should not exceed 70 characters
headers Optional. Specifies additional headers, like From, Cc, and Bcc. The additional headers should be separated with a CRLF (\r\n)
parameters Optional. Specifies an additional parameter to the send mail program

As soon as the mail function is called PHP will attempt to send the email then it will return true if successful or false if it is failed.

Multiple recipients can be specified as the first argument to the mail() function in a comma separated list.

Sending HTML email

When you send a text message using PHP then all the content will be treated as simple text. Even if you will include HTML tags in a text message, it will be displayed as simple text and HTML tags will not be formatted according to HTML syntax. But PHP provides option to send an HTML message as actual HTML message.

While sending an email message you can specify a Mime version, content type and character set to send an HTML email.

Example:

Following example will send an HTML email message to xyz@somedomain.com copying it to afgh@somedomain.com. You can code this program in such a way that it should receive all content from the user and then it should send an email.

<html>
   
   <head>
      <title>Sending HTML email using PHP</title>
   </head>
   
   <body>
      
      <?php
         $to = "xyz@somedomain.com";
         $subject = "This is subject";
         
         $message = "<b>This is HTML message.</b>";
         $message .= "<h1>This is headline.</h1>";
         
         $header = "From:abc@somedomain.com \r\n";
         $header = "Cc:afgh@somedomain.com \r\n";
         $header .= "MIME-Version: 1.0\r\n";
         $header .= "Content-type: text/html\r\n";
         
         $retval = mail ($to,$subject,$message,$header);
         
         if( $retval == true )
         {
            echo "Message sent successfully...";
         }
         else
         {
            echo "Message could not be sent...";
         }
      ?>
      
   </body>
</html>

Sending attachments with email

To send an email with mixed content requires to set Content-type header to multipart/mixed. Then text and attachment sections can be specified within boundaries.

A boundary is started with two hyphens followed by a unique number which can not appear in the message part of the email. A PHP function md5() is used to create a 32 digit hexadecimal number to create unique number. A final boundary denoting the email's final section must also end with two hyphens.

<?php
   // request variables // important
   $from=$_REQUEST["from"];
   $emaila=$_REQUEST["emaila"];
   $filea=$_REQUEST["filea"];
   
   if ($filea)
   {
      function mail_attachment ($from , $to, $subject, $message, $attachment){
         $fileatt = $attachment; // Path to the file
         $fileatt_type = "application/octet-stream"; // File Type 
         
         $start = strrpos($attachment, '/') == -1 ? strrpos($attachment, '//') : strrpos($attachment, '/')+1;
         $fileatt_name = substr($attachment, $start, strlen($attachment)); // Filename that will be used for the file as the attachment 
         
         $email_from = $from; // Who the email is from
         $subject = "New Attachment Message";
         
         $email_subject =  $subject; // The Subject of the email 
         $email_txt = $message; // Message that the email has in it 
         $email_to = $to; // Who the email is to
         
         $headers = "From: ".$email_from;
         $file = fopen($fileatt,'rb'); 
         $data = fread($file,filesize($fileatt)); 
         fclose($file); 
         
         $msg_txt="\n\n You have recieved a new attachment message from $from";
         $semi_rand = md5(time()); 
         $mime_boundary = "==Multipart_Boundary_x{$semi_rand}x"; 
         $headers .= "\nMIME-Version: 1.0\n" . "Content-Type: multipart/mixed;\n" . " boundary=\"{$mime_boundary}\"";
         
         $email_txt .= $msg_txt;
         $email_message .= "This is a multi-part message in MIME format.\n\n" . "--{$mime_boundary}\n" . "Content-Type:text/html; charset=\"iso-8859-1\"\n" . "Content-Transfer-Encoding: 7bit\n\n" . $email_txt . "\n\n";
         $data = chunk_split(base64_encode($data));
         
         $email_message .= "--{$mime_boundary}\n" . "Content-Type: {$fileatt_type};\n" . " name=\"{$fileatt_name}\"\n" . //"Content-Disposition: attachment;\n" . //" filename=\"{$fileatt_name}\"\n" . "Content-Transfer-Encoding: base64\n\n" . $data . "\n\n" . "--{$mime_boundary}--\n";
         $ok = mail($email_to, $email_subject, $email_message, $headers);
         
         if($ok)
         {
            echo "File Sent Successfully.";
            unlink($attachment); // delete a file after attachment sent.
         }
         
         else
         {
            die("Sorry but the email could not be sent. Please go back and try again!");
         }
      }
      move_uploaded_file($_FILES["filea"]["tmp_name"],'temp/'.basename($_FILES['filea']['name']));
      mail_attachment("$from", "youremailaddress@gmail.com", "subject", "message", ("temp/".$_FILES["filea"]["name"]));
   }
?>

<html>
   <head>
      
      <script language="javascript" type="text/javascript">
         function CheckData45()
         {
            with(document.filepost)
            {
               if(filea.value != "")
               {
                  document.getElementById('one').innerText = "Attaching File ... Please Wait";
               }
            }
         }
      </script>
      
   </head>
   <body>
      
      <table width="100%" height="100%" border="0" cellpadding="0" cellspacing="0">
         <tr>
            <td align="center">
               <form name="filepost" method="post" action="file.php" enctype="multipart/form-data" id="file">
                  
                  <table width="300" border="0" cellspacing="0" cellpadding="0">
                     <tr valign="bottom">
                        <td height="20">Your Name:</td>
                     </tr>
                     
                     <tr>
                        <td><input name="from" type="text" id="from" size="30"></td>
                     </tr>
                     
                     <tr valign="bottom">
                        <td height="20">Your Email Address:</td>
                     </tr>
                     
                     <tr>
                        <td class="frmtxt2"><input name="emaila" type="text" id="emaila" size="30"> </td>
                     </tr>
                     
                     <tr>
                        <td height="20" valign="bottom">Attach File:</td>
                     </tr>
                     
                     <tr valign="bottom">
                        <td valign="bottom"><input name="filea" type="file" id="filea" size="16"></td>
                     </tr>
                     
                     <tr>
                        <td height="40" valign="middle"><input name="Reset2" type="reset" id="Reset2" value="Reset">
                        <input name="Submit2" type="submit" value="Submit" onClick="return CheckData45()"></td>
                     </tr>
                  </table>
                  
               </form>
               
               <center>
                  <table width="400">
                     <tr>
                        <td id="one">
                        </td>
                     </tr>
                  </table>
               </center>
               
            </td>
         </tr>
      </table>
      
   </body>
</html>

A PHP script can be used with a HTML form to allow users to upload files to the server. Initially files are uploaded into a temporary directory and then relocated to a target destination by a PHP script.

Information in the phpinfo.php page describes the temporary directory that is used for file uploads as upload_tmp_dir and the maximum permitted size of files that can be uploaded is stated as upload_max_filesize. These parameters are set into PHP configuration file php.ini

The process of uploading a file follows these steps:

  1. The user opens the page containing a HTML form featuring a text files, a browse button and a submit button.
  2. The user clicks the browse button and selects a file to upload from the local PC.
  3. The full path to the selected file appears in the text filed then the user clicks the submit button.
  4. The selected file is sent to the temporary directory on the server.
  5. The PHP script that was specified as the form handler in the form's action attribute checks that the file has arrived and then copies the file into an intended directory.
  6. The PHP script confirms the success to the user.

As usual when writing files it is necessary for both temporary and final locations to have permissions set that enable file writing. If either is set to be read-only then process will fail.

An uploaded file could be a text file or image file or any document.

Creating an upload form

The following HTM code below creates an uploader form. This form is having method attribute set to post and enctype attribute is set to multipart/form-data

<?php
   if(isset($_FILES['image'])){
      $errors= array();
      $file_name = $_FILES['image']['name'];
      $file_size =$_FILES['image']['size'];
      $file_tmp =$_FILES['image']['tmp_name'];
      $file_type=$_FILES['image']['type'];
      $file_ext=strtolower(end(explode('.',$_FILES['image']['name'])));
      
      $expensions= array("jpeg","jpg","png");
      
      if(in_array($file_ext,$expensions)=== false){
         $errors[]="extension not allowed, please choose a JPEG or PNG file.";
      }
      
      if($file_size > 2097152){
         $errors[]='File size must be excately 2 MB';
      }
      
      if(empty($errors)==true){
         move_uploaded_file($file_tmp,"images/".$file_name);
         echo "Success";
      }
      else{
         print_r($errors);
      }
   }
?>
<html>
   <body>
      
      <form action="" method="POST" enctype="multipart/form-data">
         <input type="file" name="image" />
         <input type="submit"/>
      </form>
      
   </body>
</html>

It will produce the following result:

Creating an upload script

There is one global PHP variable called $_FILES. This variable is an associate double dimension array and keeps all the information related to uploaded file. So if the value assigned to the input's name attribute in uploading form was file, then PHP would create following five variables

  1. $_FILES['file']['tmp_name']: The uploaded file in the temporary directory on the web server.
  2. $_FILES['file']['name']: The actual name of the uploaded file.
  3. $_FILES['file']['size']: he size in bytes of the uploaded file.
  4. $_FILES['file']['type']: The MIME type of the uploaded file.
  5. $_FILES['file']['error']: The error code associated with this file upload.

Example

Below example should allow upload images and gives back result as uploaded file information.

<?php
   if(isset($_FILES['image'])){
      $errors= array();
      $file_name = $_FILES['image']['name'];
      $file_size =$_FILES['image']['size'];
      $file_tmp =$_FILES['image']['tmp_name'];
      $file_type=$_FILES['image']['type'];
      $file_ext=strtolower(end(explode('.',$_FILES['image']['name'])));
      
      $expensions= array("jpeg","jpg","png");
      
      if(in_array($file_ext,$expensions)=== false){
         $errors[]="extension not allowed, please choose a JPEG or PNG file.";
      }
      
      if($file_size > 2097152){
         $errors[]='File size must be excately 2 MB';
		}
      
      if(empty($errors)==true){
         move_uploaded_file($file_tmp,"images/".$file_name);
         echo "Success";
      }
      else{
         print_r($errors);
      }
   }
?>
<html>
   <body>
      
      <form action="" method="POST" enctype="multipart/form-data">
         <input type="file" name="image" />
         <input type="submit"/>
			
         <ul>
            <li>Sent file: <?php echo $_FILES['image']['name'];  ?>
            <li>File size: <?php echo $_FILES['image']['size'];  ?>
            <li>File type: <?php echo $_FILES['image']['type'] ?>
         </ul>
			
      </form>
      
   </body>
</html>

It will produce the following result:

PHP provides a large number of predefined variables to any script which it runs. PHP provides an additional set of predefined arrays containing variables from the web server the environment, and user input. These new arrays are called superglobals

All the following variables are automatically available in every scope.

PHP Superglobals

Variable Description
$GLOBALS Contains a reference to every variable which is currently available within the global scope of the script. The keys of this array are the names of the global variables.
$_SERVER This is an array containing information such as headers, paths, and script locations. The entries in this array are created by the web server. There is no guarantee that every web server will provide any of these. See next section for a complete list of all the SERVER variables.
$_GET An associative array of variables passed to the current script via the HTTP GET method.
$_POST An associative array of variables passed to the current script via the HTTP POST method.
$_FILES An associative array of items uploaded to the current script via the HTTP POST method.
$_REQUEST An associative array consisting of the contents of $_GET, $_POST, and $_COOKIE.
$_COOKIE An associative array of variables passed to the current script via HTTP cookies.
$_SESSION An associative array containing session variables available to the current script.
$_PHP_SELF A string containing PHP script file name in which it is called.
$php_errormsg $php_errormsg is a variable containing the text of the last error message generated by PHP.

Server variables: $_SERVER

$_SERVER is an array containing information such as headers, paths, and script locations. The entries in this array are created by the web server. There is no guarantee that every web server will provide any of these.

Variable Description
$_SERVER['PHP_SELF'] The filename of the currently executing script, relative to the document root.
$_SERVER['argv'] Array of arguments passed to the script. When the script is run on the command line, this gives C-style access to the command line parameters. When called via the GET method, this will contain the query string.
$_SERVER['argc'] Contains the number of command line parameters passed to the script if run on the command line.
$_SERVER['GATEWAY_INTERFACE'] What revision of the CGI specification the server is using; i.e. 'CGI/1.1'.
$_SERVER['SERVER_ADDR'] The IP address of the server under which the current script is executing.
$_SERVER['SERVER_NAME'] The name of the server host under which the current script is executing. If the script is running on a virtual host, this will be the value defined for that virtual host.
$_SERVER['SERVER_SOFTWARE'] Server identification string, given in the headers when responding to requests.
$_SERVER['SERVER_PROTOCOL'] Name and revision of the information protocol via which the page was requested; i.e. 'HTTP/1.0';
$_SERVER['REQUEST_METHOD'] Which request method was used to access the page; i.e. 'GET', 'HEAD', 'POST', 'PUT'.
$_SERVER['REQUEST_TIME'] The timestamp of the start of the request. Available since PHP 5.1.0.
$_SERVER['QUERY_STRING'] The query string, if any, via which the page was accessed.
$_SERVER['DOCUMENT_ROOT'] The document root directory under which the current script is executing, as defined in the server's configuration file.
$_SERVER['HTTP_ACCEPT'] Contents of the Accept: header from the current request, if there is one.
$_SERVER['HTTP_ACCEPT_CHARSET'] Contents of the Accept-Charset: header from the current request, if there is one. Example: 'iso-8859-1,*,utf-8'.
$_SERVER['HTTP_ACCEPT_ENCODING'] Contents of the Accept-Encoding: header from the current request, if there is one. Example: 'gzip'.
$_SERVER['HTTP_ACCEPT_LANGUAGE'] Contents of the Accept-Language: header from the current request, if there is one. Example: 'en'.
$_SERVER['HTTP_CONNECTION'] Contents of the Connection: header from the current request, if there is one. Example: 'Keep-Alive'.
$_SERVER['HTTP_HOST'] Contents of the Host: header from the current request, if there is one.
$_SERVER['HTTP_REFERER'] The address of the page (if any) which referred the user agent to the current page.
$_SERVER['HTTP_USER_AGENT'] This is a string denoting the user agent being which is accessing the page. A typical example is: Mozilla/4.5 [en] (X11; U; Linux 2.2.9 i586).
$_SERVER['HTTPS'] Set to a non-empty value if the script was queried through the HTTPS protocol.
$_SERVER['REMOTE_ADDR'] The IP address from which the user is viewing the current page.
$_SERVER['REMOTE_HOST'] The Host name from which the user is viewing the current page. The reverse dns lookup is based off the REMOTE_ADDR of the user.
$_SERVER['REMOTE_PORT'] The port being used on the user's machine to communicate with the web server.
$_SERVER['SCRIPT_FILENAME'] The absolute pathname of the currently executing script.
$_SERVER['SERVER_ADMIN'] The value given to the SERVER_ADMIN (for Apache) directive in the web server configuration file.
$_SERVER['SERVER_PORT'] The port on the server machine being used by the web server for communication. For default setups, this will be '80'.
$_SERVER['SERVER_SIGNATURE'] String containing the server version and virtual host name which are added to server-generated pages, if enabled.
$_SERVER['PATH_TRANSLATED'] Filesystem based path to the current script.
$_SERVER['SCRIPT_NAME'] Contains the current script's path. This is useful for pages which need to point to themselves.
$_SERVER['REQUEST_URI'] The URI which was given in order to access this page; for instance, '/index.html'.
$_SERVER['PHP_AUTH_DIGEST'] When running under Apache as module doing Digest HTTP authentication this variable is set to the 'Authorization' header sent by the client.
$_SERVER['PHP_AUTH_USER'] When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the username provided by the user.
$_SERVER['PHP_AUTH_PW'] When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the password provided by the user.
$_SERVER['AUTH_TYPE'] When running under Apache as module doing HTTP authenticated this variable is set to the authentication type.

Regular expressions are nothing more than a sequence or pattern of characters itself. They provide the foundation for pattern-matching functionality.

Using regular expression you can search a particular string inside a another string, you can replace one string by another string and you can split a string into many chunks.

PHP offers functions specific to two sets of regular expression functions, each corresponding to a certain type of regular expression. You can use any of them based on your comfort.

  1. POSIX Regular Expressions
  2. PERL Style Regular Expressions

POSIX Regular Expressions

The structure of a POSIX regular expression is not dissimilar to that of a typical arithmetic expression: various elements (operators) are combined to form more complex expressions.

The simplest regular expression is one that matches a single character, such as g, inside strings such as g, haggle, or bag.

Lets give explanation for few concepts being used in POSIX regular expression. After that we will introduce you with regular expression related functions.

Brackets

Brackets ([]) have a special meaning when used in the context of regular expressions. They are used to find a range of characters.

Expression Description
[0-9] It matches any decimal digit from 0 through 9.
[a-z] It matches any character from lower-case a through lowercase z.
[A-Z] It matches any character from uppercase A through uppercase Z.
[a-Z] It matches any character from lowercase a through uppercase Z.

The ranges shown above are general; you could also use the range [0-3] to match any decimal digit ranging from 0 through 3, or the range [b-v] to match any lowercase character ranging from b through v.

Quantifiers

The frequency or position of bracketed character sequences and single characters can be denoted by a special character. Each special character having a specific connotation. The +, *, ?, {int. range}, and $ flags all follow a character sequence.

Expression Description
p+ It matches any string containing at least one p.
p* It matches any string containing zero or more p's.
p? It matches any string containing zero or more p's. This is just an alternative way to use p*.
p{N} It matches any string containing a sequence of N p's
p{2,3} It matches any string containing a sequence of two or three p's.
p{2, } It matches any string containing a sequence of at least two p's.
p$ It matches any string with p at the end of it.
^p It matches any string with p at the beginning of it.

Examples:

Following examples will clear your concepts about matching characters.

Expression Description
[^a-zA-Z] It matches any string not containing any of the characters ranging from a through z and A through Z.
p.p It matches any string containing p, followed by any character, in turn followed by another p.
^.{2}$ It matches any string containing exactly two characters.
<b>(.*)</b> It matches any string enclosed within <b> and </b>.
p(hp)* It matches any string containing a p followed by zero or more instances of the sequence php.

Predefined Character Ranges

For your programming convenience several predefined character ranges, also known as character classes, are available. Character classes specify an entire range of characters, for example, the alphabet or an integer se

Expression Description
[[:alpha:]] It matches any string containing alphabetic characters aA through zZ.
[[:digit:]] It matches any string containing numerical digits 0 through 9.
[[:alnum:]] It matches any string containing alphanumeric characters aA through zZ and 0 through 9.
[[:space:]] It matches any string containing a space.

PHP's Regexp POSIX Functions

PHP currently offers seven functions for searching strings using POSIX-style regular expressions:

Function Description
ereg() The ereg() function searches a string specified by string for a string specified by pattern, returning true if the pattern is found, and false otherwise.
ereg_replace() The ereg_replace() function searches for string specified by pattern and replaces pattern with replacement if found.
eregi() The eregi() function searches throughout a string specified by pattern for a string specified by string. The search is not case sensitive.
eregi_replace() The eregi_replace() function operates exactly like ereg_replace(), except that the search for pattern in string is not case sensitive.
split() The split() function will divide a string into various elements, the boundaries of each element based on the occurrence of pattern in string.
spliti() The spliti() function operates exactly in the same manner as its sibling split(), except that it is not case sensitive.
sql_regcase() The sql_regcase() function can be thought of as a utility function, converting each character in the input parameter string into a bracketed expression containing two characters.

PERL Style Regular Expressions

Perl-style regular expressions are similar to their POSIX counterparts. The POSIX syntax can be used almost interchangeably with the Perl-style regular expression functions. In fact, you can use any of the quantifiers introduced in the previous POSIX section.

Lets give explanation for few concepts being used in PERL regular expressions. After that we will introduce you wih regular expression related functions.

Meta characters

A meta character is simply an alphabetical character preceded by a backslash that acts to give the combination a special meaning.

For instance, you can search for large money sums using the '\d' meta character: /([\d]+)000/, Here \d will search for any string of numerical character.

Following is the list of meta characters which can be used in PERL Style Regular Expressions.

Character		Description
.              a single character
\s             a whitespace character (space, tab, newline)
\S             non-whitespace character
\d             a digit (0-9)
\D             a non-digit
\w             a word character (a-z, A-Z, 0-9, _)
\W             a non-word character
[aeiou]        matches a single character in the given set
[^aeiou]       matches a single character outside the given set
(foo|bar|baz)  matches any of the alternatives specified

Modifiers

Several modifiers are available that can make your work with regexps much easier, like case sensitivity, searching in multiple lines etc.

Modifier	Description
i 	Makes the match case insensitive
m 	Specifies that if the string has newline or carriage
	return characters, the ^ and $ operators will now
	match against a newline boundary, instead of a
	string boundary
o 	Evaluates the expression only once
s 	Allows use of . to match a newline character
x 	Allows you to use white space in the expression for clarity
g 	Globally finds all matches
cg 	Allows a search to continue even after a global match fails

PHP's Regexp PERL Compatible Functions

PHP offers following functions for searching strings using Perl-compatible regular expressions:

Function Description
preg_match() The preg_match() function searches string for pattern, returning true if pattern exists, and false otherwise.
preg_match_all() The preg_match_all() function matches all occurrences of pattern in string.
preg_replace() The preg_replace() function operates just like ereg_replace(), except that regular expressions can be used in the pattern and replacement input parameters.
preg_split() The preg_split() function operates exactly like split(), except that regular expressions are accepted as input parameters for pattern.
preg_grep() The preg_grep() function searches all elements of input_array, returning all elements matching the regexp pattern.
preg_quote() Quote regular expression characters

Error handling is the process of catching errors raised by your program and then taking appropriate action. If you would handle errors properly then it may lead to many unforeseen consequences.

Its very simple in PHP to handle an errors.

Using die() function

While writing your PHP program you should check all possible error condition before going ahead and take appropriate action when required.

Try following example without having /tmp/test.xt file and with this file.

<?php
   if(!file_exists("/tmp/test.txt"))
   {
      die("File not found");
   }
   else
   {
      $file=fopen("/tmp/test.txt","r");
      print "Opend file sucessfully";
   }
   // Test of the code here.
?>

This way you can write an efficient code. Using above technique you can stop your program whenever it errors out and display more meaningful and user friendly message.

Defining Custom Error Handling Function

You can write your own function to handling any error. PHP provides you a framework to define error handling function.

This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters (optionally: file, line-number, and the error context)

Syntax

error_function(error_level,error_message, error_file,error_line,error_context);
Parameter Description
error_level Required - Specifies the error report level for the user-defined error. Must be a value number.
error_message Required - Specifies the error message for the user-defined error.
error_file Optional - Specifies the file name in which the error occurred.
error_line Optional - Specifies the line number in which the error occurred.
error_context Optional - Specifies an array containing every variable and their values in use when the error occurred

Possible Error levels

These error report levels are the different types of error the user-defined error handler can be used for. These values cab used in combination using | operator

Value Constant Description
1 E_ERROR Fatal run-time errors. Execution of the script is halted.
2 E_WARNING Non-fatal run-time errors. Execution of the script is not halted.
4 E_PARSE Compile-time parse errors. Parse errors should only be generated by the parser.
8 E_NOTICE Run-time notices. The script found something that might be an error, but could also happen when running a script normally.
16 E_CORE_ERROR Fatal errors that occur during PHP's initial start-up.
32 E_CORE_WARNING Non-fatal run-time errors. This occurs during PHP's initial start-up.
256 E_USER_ERROR Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()
512 E_USER_WARNING Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()
1024 E_USER_NOTICE User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()
2048 E_STRICT Run-time notices. Enable to have PHP suggest changes to your code which will ensure the best interoperability and forward compatibility of your code.
4096 E_RECOVERABLE_ERROR Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())
8191 E_ALL All errors and warnings, except level E_STRICT (E_STRICT will be part of E_ALL as of PHP 6.0)

All the above error level can be set using following PHP built-in library function where level cab be any of the value defined in above table.

int error_reporting ( [int $level] )

Following is the way you can create one error handling function:

<?php
   function handleError($errno, $errstr,$error_file,$error_line)
   {
      echo "<b>Error:</b> [$errno] $errstr - $error_file:$error_line";
      echo "<br />";
      echo "Terminating PHP Script";
      die();
   }
?>

Once you define your custom error handler you need to set it using PHP built-in library set_error_handler function. Now lets examine our example by calling a function which does not exist.

<?php
   error_reporting( E_ERROR );
   
   function handleError($errno, $errstr,$error_file,$error_line)
   {
      echo "<b>Error:</b> [$errno] $errstr - $error_file:$error_line";
      echo "<br />";
      echo "Terminating PHP Script";
      die();
   }
   
   //set error handler
   set_error_handler("handleError");
   
   //trigger error
   myFunction();
?>

Exceptions Handling

PHP 5 has an exception model similar to that of other programming languages. Exceptions are important and provides a better control over error handling.

Lets explain there new keyword related to exceptions.

  1. Try: A function using an exception should be in a "try" block. If the exception does not trigger, the code will continue as normal. However if the exception triggers, an exception is "thrown".
  2. Throw: This is how you trigger an exception. Each "throw" must have at least one "catch".
  3. Catch: A "catch" block retrieves an exception and creates an object containing the exception information.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception

  1. An exception can be thrown, and caught ("catched") within PHP. Code may be surrounded in a try block.
  2. Each try must have at least one corresponding catch block. Multiple catch blocks can be used to catch different classes of exceptions.
  3. Exceptions can be thrown (or re-thrown) within a catch block.

Example:

Following is the piece of code, copy and paste this code into a file and verify the result.

<?php
   try {
      $error = 'Always throw this error';
      throw new Exception($error);
      
      // Code following an exception is not executed.
      echo 'Never executed';
   }
   catch (Exception $e) {
      echo 'Caught exception: ',  $e->getMessage(), "\n";
   }
   
   // Continue execution
   echo 'Hello World';
?>

In the above example $e->getMessage function is used to get error message. There are following functions which can be used from Exception class.

  1. getMessage() − message of exception
  2. getCode() − code of exception
  3. getFile() − source filename
  4. getLine() − source line
  5. getTrace() − n array of the backtrace()
  6. getTraceAsString() − formated string of trace

Creating Custom Exception Handler

You can define your own custom exception handler. Use following function to set a user-defined exception handler function.

string set_exception_handler ( callback $exception_handler )

Here exception_handler is the name of the function to be called when an uncaught exception occurs. This function must be defined before calling set_exception_handler().

Example:

<?php
   function exception_handler($exception) {
      echo "Uncaught exception: " , $exception->getMessage(), "\n";
   }
   set_exception_handler('exception_handler');
   throw new Exception('Uncaught Exception');
   
   echo "Not Executed\n";
?>

Programs rarely work correctly the first time. Many things can go wrong in your program that cause the PHP interpreter to generate an error message. You have a choice about where those error messages go. The messages can be sent along with other program output to the web browser. They can also be included in the web server error log.

To make error messages display in the browser, set the display_errors configuration directive to On. To send errors to the web server error log, set log_errors to On. You can set them both to On if you want error messages in both places.

PHP defines some constants you can use to set the value of error_reporting such that only errors of certain types get reported: E_ALL (for all errors except strict notices), E_PARSE (parse errors), E_ERROR (fatal errors), E_WARNING (warnings), E_NOTICE (notices), and E_STRICT (strict notices).

While writing your PHP program, it is a good idea to use PHP-aware editors like BBEdit or Emacs. One of the special special features of these editors is syntax highlighting. It changes the color of different parts of your program based on what those parts are. For example, strings are pink, keywords such as if and while are blue, comments are grey, and variables are black.

Another feature is quote and bracket matching, which helps to make sure that your quotes and brackets are balanced. When you type a closing delimiter such as }, the editor highlights the opening { that it matches.

There are following points which need to be verified while debugging your program.

  1. Missing Semicolons: Every PHP statement ends with a semicolon (;). PHP doesn't stop reading a statement until it reaches a semicolon. If you leave out the semicolon at the end of a line, PHP continues reading the statement on the following line.
  2. Not Enough Equal Signs: When you ask whether two values are equal in a comparison statement, you need two equal signs (==). Using one equal sign is a common mistake.
  3. Misspelled Variable Names: If you misspelled a variable then PHP understands it as a new variable. Remember: To PHP, $test is not the same variable as $Test.
  4. Missing Dollar Signs: A missing dollar sign in a variable name is really hard to see, but at least it usually results in an error message so that you know where to look for the problem.
  5. Troubling Quotes: You can have too many, too few, or the wrong kind of quotes. So check for a balanced number of quotes.
  6. Missing Parentheses and curly brackets: They should always be in pairs.
  7. Array Index: All the arrays should start from zero instead of 1.

Moreover, handle all the errors properly and direct all trace messages into system log file so that if any problem happens then it will be logged into system log file and you will be able to debug that problem.

Dates are so much part of everyday life that it becomes easy to work with them without thinking. PHP also provides powerful tools for date arithmetic that make manipulating dates easy.

Getting the Time Stamp with time()

PHP's time() function gives you all the information that you need about the current date and time. It requires no arguments but returns an integer.

The integer returned by time() represents the number of seconds elapsed since midnight GMT on January 1, 1970. This moment is known as the UNIX epoch, and the number of seconds that have elapsed since then is referred to as a time stamp.

<?php
   print time();
?>

This will produce the following result

1444438327

This is something difficult to understand. But PHP offers excellent tools to convert a time stamp into a form that humans are comfortable with.

Converting a Time Stamp with getdate()

The function getdate() optionally accepts a time stamp and returns an associative array containing information about the date. If you omit the time stamp, it works with the current time stamp as returned by time().

Following table lists the elements contained in the array returned by getdate().

Key Description Example
seconds Seconds past the minutes (0-59) 20
minutes Minutes past the hour (0 - 59) 29
hours Hours of the day (0 - 23) 22
mday Day of the month (1 - 31) 11
wday Day of the week (0 - 6) 4
mon Month of the year (1 - 12) 7
year Year (4 digits) 1997
yday Day of year ( 0 - 365 ) 19
weekday Day of the week Thursday
month Month of the year January
0 Timestamp 948370048

Now you have complete control over date and time. You can format this date and time in whatever format you wan.

Example:

Try out following example

<?php
   $date_array = getdate();
   
   foreach ( $date_array as $key => $val )
   {
      print "$key = $val<br />";
   }
	
   $formated_date  = "Today's date: ";
   $formated_date .= $date_array['mday'] . "/";
   $formated_date .= $date_array['mon'] . "/";
   $formated_date .= $date_array['year'];
   
   print $formated_date;
?>

It will produce following result

seconds = 1
minutes = 32
hours = 7
mday = 14
wday = 6
mon = 12
year = 2019
yday = 347
weekday = Saturday
month = December
0 = 1576326721
Today's date: 14/12/2019

Converting a Time Stamp with date()

The date() function returns a formatted string representing a date. You can exercise an enormous amount of control over the format that date() returns with a string argument that you must pass to it.

date(format,timestamp)

The date() optionally accepts a time stamp if omitted then current date and time will be used. Any other data you include in the format string passed to date() will be included in the return value.

Following table lists the codes that a format string can contain:

Format Description Example
a 'am' or 'pm' lowercase pm
A 'AM' or 'PM' uppercase PM
d Day of month, a number with leading zeroes 20
D Day of week (three letters) Thu
F Month name January
h Hour (12-hour format - leading zeroes) 12
H Hour (24-hour format - leading zeroes) 22
seconds Seconds past the minutes (0-59) 20
g Hour (12-hour format - no leading zeroes) 12
G Hour (24-hour format - no leading zeroes) 22
i Minutes ( 0 - 59 ) 23
j Day of the month (no leading zeroes) 20
l (Lower 'L') Day of the week Thursday
L Leap year ('1' for yes, '0' for no) 1
m Month of year (number - leading zeroes) 1
M Month of year (three letters) Jan
r The RFC 2822 formatted date Thu, 21 Dec 2000 16:01:07 +0200
n Month of year (number - no leading zeroes) 2
s Seconds of hour 20
U Time stamp 948372444
y Year (two digits) 06
Y Year (four digits) 2006
z Day of year (0 - 365) 206
Z Offset in seconds from GMT +5

Example:

Try out following example:

<?php
   print date("m/d/y G.i:s<br>", time());
   print "Today is ";
   print date("j of F Y, \a\\t g.i a", time());
?>

It will produce following result:

12/14/19 7.32:01Today is 14 2019f December 2019, at 7.32 am

Hope you have good understanding on how to format date and time according to your requirement.

PHP will work with virtually all database software, including Oracle and Sybase but most commonly used is freely available MySQL database.

What you should already have?

  1. You have gone through MySQL tutorial to understand MySQL Basics.
  2. Downloaded and installed a latest version of MySQL.
  3. Created database user guest with password guest123.
  4. If you have not created a database then you would need root user and its password to create a database.

We have divided this chapter in the following sections:

  1. MySQL Database Connection

    Opening Database Connection

    PHP provides mysql_connect function to open a database connection. This function takes five parameters and returns a MySQL link identifier on success, or FALSE on failure.

    Syntax

    connection mysql_connect(server,user,passwd,new_link,client_flag);
    Parameter Description
    server Optional - The host name running database server. If not specified then default value is localhost:3306.
    user Optional - The username accessing the database. If not specified then default is the name of the user that owns the server process.
    passwd Optional - The password of the user accessing the database. If not specified then default is an empty password.
    new_link Optional − If a second call is made to mysql_connect() with the same arguments, no new connection will be established; instead, the identifier of the already opened connection will be returned.
    client_flags Optional − A combination of the following constants
    1. MYSQL_CLIENT_SSL − Use SSL encryption
    2. MYSQL_CLIENT_COMPRESS − Use compression protocol
    3. MYSQL_CLIENT_IGNORE_SPACE − Allow space after function names
    4. MYSQL_CLIENT_INTERACTIVE − Allow interactive timeout seconds of inactivity before closing the connection

    NOTE: You can specify server, user, passwd in php.ini file instead of using them again and again in your every PHP scripts. Check php.ini file configuration.

    Closing Database Connection

    Its simplest function mysql_close PHP provides to close a database connection. This function takes connection resource returned by mysql_connect function. It returns TRUE on success or FALSE on failure.

    Syntax

    bool mysql_close ( resource $link_identifier );

    If a resource is not specified then last opend database is closed.

    Example:

    Try out following example to open and close a database connection:

    <?php
       
       $dbhost = 'localhost:3036';
       $dbuser = 'guest';
       $dbpass = 'guest123';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       echo 'Connected successfully';
       mysql_close($conn);
    ?>
    
  2. Create MySQL Database Using PHP

    Creating a Database

    To create and delete a database you should have admin privilege. Its very easy to create a new MySQL database. PHP uses mysql_query function to create a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.

    Syntax

    bool mysql_query( sql, connection );
    Parameter Description
    sql Required - SQL query to create a database
    connection Optional - if not specified then last opend connection by mysql_connect will be used.

    Example:

    Try out following example to create a database:

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       echo 'Connected successfully';
       
       $sql = 'CREATE Database test_db';
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not create database: ' . mysql_error());
       }
       
       echo "Database test_db created successfully\n";
       mysql_close($conn);
    ?>
    

    Selecting a Database

    Once you establish a connection with a database server then it is required to select a particular database where your all the tables are associated.

    This is required because there may be multiple databases residing on a single server and you can do work with a single database at a time.

    PHP provides function mysql_select_db to select a database.It returns TRUE on success or FALSE on failure.

    Syntax

    bool mysql_select_db( db_name, connection );
    Parameter Description
    db_name Required - Database name to be selected
    connection Optional - if not specified then last opend connection by mysql_connect will be used.

    Example:

    Here is the example showing you how to select a database.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'guest';
       $dbpass = 'guest123';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       echo 'Connected successfully';
       
       mysql_select_db( 'test_db' );
       mysql_close($conn);
       
    ?>
    

    Creating Database Tables

    To create tables in the new database you need to do the same thing as creating the database. First create the SQL query to create the tables then execute the query using mysql_query() function.

    Example:

    Try out following example to create a table.

    <?php
       
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       echo 'Connected successfully';
       
       $sql = 'CREATE TABLE employee( '.
          'emp_id INT NOT NULL AUTO_INCREMENT, '.
          'emp_name VARCHAR(20) NOT NULL, '.
          'emp_address  VARCHAR(20) NOT NULL, '.
          'emp_salary   INT NOT NULL, '.
          'join_date    timestamp(14) NOT NULL, '.
          'primary key ( emp_id ))';
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not create table: ' . mysql_error());
       }
       
       echo "Table employee created successfully\n";
       
       mysql_close($conn);
    ?>
    

    In case you need to create many tables then its better to create a text file first and put all the SQL commands in that text file and then load that file into $sql variable and excute those commands.

    Consider the following content in sql_query.txt file

    CREATE TABLE employee(
       emp_id INT NOT NULL AUTO_INCREMENT,
       emp_name VARCHAR(20) NOT NULL,
       emp_address  VARCHAR(20) NOT NULL,
       emp_salary   INT NOT NULL,
       join_date    timestamp(14) NOT NULL,
       primary key ( emp_id ));
    
    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $query_file = 'sql_query.txt';
       
       $fp    = fopen($query_file, 'r');
       $sql = fread($fp, filesize($query_file));
       fclose($fp); 
       
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not create table: ' . mysql_error());
       }
       
       echo "Table employee created successfully\n";
       mysql_close($conn);
    ?>									
    
  3. Deleting MySQL Database Using PHP

    Deleting a Database

    If a database is no longer required then it can be deleted forever. You can use pass an SQL command to mysql_query to delete a database.

    Example:

    Try out following example to drop a database.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'DROP DATABASE test_db';
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not delete database db_test: ' . mysql_error());
       }
       
       echo "Database deleted successfully\n";
       
       mysql_close($conn);
    ?>
    

    WARNING: Its very dangerous to delete a database and any table. So before deleting any table or database you should make sure you are doing everything intentionally.

    Deleting a Table

    Its again a matter of issuing one SQL command through mysql_query function to delete any database table. But be very careful while using this command because by doing so you can delete some important information you have in your table.

    Example:

    Try out following example to drop a table.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'DROP TABLE employee';
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not delete table employee: ' . mysql_error());
       }
       
       echo "Table deleted successfully\n";
       
       mysql_close($conn);
    ?>
    
  4. Insert Data into MySQL Database

    Data can be entered into MySQL tables by executing SQL INSERT statement through PHP function mysql_query. Below a simple example to insert a record into employee table.

    Example:

    Try out following example to insert record into employee table.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'INSERT INTO employee '.
          '(emp_name,emp_address, emp_salary, join_date) '.
          'VALUES ( "guest", "XYZ", 2000, NOW() )';
          
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not enter data: ' . mysql_error());
       }
       
       echo "Entered data successfully\n";
       
       mysql_close($conn);
    ?>
    

    In real application, all the values will be taken using HTML form and then those values will be captured using PHP script and finally they will be inserted into MySQL tables.

    While doing data insert its best practice to use function get_magic_quotes_gpc() to check if current configuration for magic quote is set or not. If this function returns false then use function addslashes() to add slashes before quotes.

    Example:

    Try out this example by putting this code into add_employee.php, this will take input using HTML Form and then it will create records into database.

    <html>
       
       <head>
          <title>Add New Record in MySQL Database</title>
       </head>
       
       <body>
          <?php
             if(isset($_POST['add']))
             {
                $dbhost = 'localhost:3036';
                $dbuser = 'root';
                $dbpass = 'rootpassword';
                $conn = mysql_connect($dbhost, $dbuser, $dbpass);
                
                if(! $conn )
                {
                   die('Could not connect: ' . mysql_error());
                }
                
                if(! get_magic_quotes_gpc() )
                {
                   $emp_name = addslashes ($_POST['emp_name']);
                   $emp_address = addslashes ($_POST['emp_address']);
                }
                else
                {
                   $emp_name = $_POST['emp_name'];
                   $emp_address = $_POST['emp_address'];
                }
                
                $emp_salary = $_POST['emp_salary'];
                
                $sql = "INSERT INTO employee ". "(emp_name,emp_address, emp_salary, join_date) ". "VALUES('$emp_name','$emp_address',$emp_salary, NOW())";
                   
                mysql_select_db('test_db');
                $retval = mysql_query( $sql, $conn );
                
                if(! $retval )
                {
                   die('Could not enter data: ' . mysql_error());
                }
                
                echo "Entered data successfully\n";
                
                mysql_close($conn);
             }
             else
             {
                ?>
                
                   <form method="post" action="<?php $_PHP_SELF ?>">
                      <table width="400" border="0" cellspacing="1" cellpadding="2">
                      
                         <tr>
                            <td width="100">Employee Name</td>
                            <td><input name="emp_name" type="text" id="emp_name"></td>
                         </tr>
                      
                         <tr>
                            <td width="100">Employee Address</td>
                            <td><input name="emp_address" type="text" id="emp_address"></td>
                         </tr>
                      
                         <tr>
                            <td width="100">Employee Salary</td>
                            <td><input name="emp_salary" type="text" id="emp_salary"></td>
                         </tr>
                      
                         <tr>
                            <td width="100"> </td>
                            <td> </td>
                         </tr>
                      
                         <tr>
                            <td width="100"> </td>
                            <td>
                               <input name="add" type="submit" id="add" value="Add Employee">
                            </td>
                         </tr>
                      
                      </table>
                   </form>
                
                <?php
             }
          ?>
       
       </body>
    </html>
    
  5. Getting Data From MySQL Database

    Data can be fetched from MySQL tables by executing SQL SELECT statement through PHP function mysql_query. You have several options to fetch data from MySQL.

    The most frequently used option is to use function mysql_fetch_array(). This function returns row as an associative array, a numeric array, or both. This function returns FALSE if there are no more rows.

    Below is a simple example to fetch records from employee table.

    Example:

    Try out following example to display all the records from employee table.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'SELECT emp_id, emp_name, emp_salary FROM employee';
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not get data: ' . mysql_error());
       }
       
       while($row = mysql_fetch_array($retval, MYSQL_ASSOC))
       {
          echo "EMP ID :{$row['emp_id']}  <br> ".
             "EMP NAME : {$row['emp_name']} <br> ".
             "EMP SALARY : {$row['emp_salary']} <br> ".
             "--------------------------------<br>";
       }
       
       echo "Fetched data successfully\n";
       
       mysql_close($conn);
    ?>
    

    The content of the rows are assigned to the variable $row and the values in row are then printed.

    NOTE: Always remember to put curly brackets when you want to insert an array value directly into a string.

    In above example the constant MYSQL_ASSOC is used as the second argument to mysql_fetch_array(), so that it returns the row as an associative array. With an associative array you can access the field by using their name instead of using the index.

    PHP provides another function called mysql_fetch_assoc() which also returns the row as an associative array.

    Example:

    Try out following example to display all the records from employee table using mysql_fetch_assoc() function.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'SELECT emp_id, emp_name, emp_salary FROM employee';
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not get data: ' . mysql_error());
       }
       
       while($row = mysql_fetch_assoc($retval))
       {
          echo "EMP ID :{$row['emp_id']}  <br> ".
             "EMP NAME : {$row['emp_name']} <br> ".
             "EMP SALARY : {$row['emp_salary']} <br> ".
             "--------------------------------<br>";
       }
       
       echo "Fetched data successfully\n";
       
       mysql_close($conn);
    ?>
    

    You can also use the constant MYSQL_NUM, as the second argument to mysql_fetch_array(). This will cause the function to return an array with numeric index.

    Example:

    Try out following example to display all the records from employee table using MYSQL_NUM argument.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'SELECT emp_id, emp_name, emp_salary FROM employee';
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not get data: ' . mysql_error());
       }
       
       while($row = mysql_fetch_array($retval, MYSQL_NUM))
       {
          echo "EMP ID :{$row[0]}  <br> ".
             "EMP NAME : {$row[1]} <br> ".
             "EMP SALARY : {$row[2]} <br> ".
             "--------------------------------<br>";
       }
       
       echo "Fetched data successfully\n";
       
       mysql_close($conn);
    ?>
    

    All the above three examples will produce same result.

    Releasing Memory

    Its a good practice to release cursor memory at the end of each SELECT statement. This can be done by using PHP function mysql_free_result(). Below is the example to show how it has to be used.

    Example:

    Try out following example

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
       
       $sql = 'SELECT emp_id, emp_name, emp_salary FROM employee';
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not get data: ' . mysql_error());
       }
       
       while($row = mysql_fetch_array($retval, MYSQL_NUM))
       {
          echo "EMP ID :{$row[0]}  <br> ".
             "EMP NAME : {$row[1]} <br> ".
             "EMP SALARY : {$row[2]} <br> ".
             "--------------------------------<br>";
       }
       
       mysql_free_result($retval);
       echo "Fetched data successfully\n";
       
       mysql_close($conn);
    ?>
    

    While fetching data you can write as complex SQL as you like. Procedure will remain same as mentioned above.

  6. Using Paging through PHP

    Its always possible that your SQL SELECT statement query may result into thousand of records. But its is not good idea to display all the results on one page. So we can divide this result into many pages as per requirement.

    Paging means showing your query result in multiple pages instead of just put them all in one long page.

    MySQL helps to generate paging by using LIMIT clause which will take two arguments. First argument as OFFSET and second argument how many records should be returned from the database.

    Below is a simple example to fetch records using LIMIT clause to generate paging.

    Example:

    Try out following example to display 10 records per page.

    <html>
       
       <head>
          <title>Paging Using PHP</title>
       </head>
       
       <body>
          <?php
             $dbhost = 'localhost:3036';
             $dbuser = 'root';
             $dbpass = 'rootpassword';
             
             $rec_limit = 10;
             $conn = mysql_connect($dbhost, $dbuser, $dbpass);
             
             if(! $conn )
             {
                die('Could not connect: ' . mysql_error());
             }
             mysql_select_db('test_db');
             
             /* Get total number of records */
             $sql = "SELECT count(emp_id) FROM employee ";
             $retval = mysql_query( $sql, $conn );
             
             if(! $retval )
             {
                die('Could not get data: ' . mysql_error());
             }
             $row = mysql_fetch_array($retval, MYSQL_NUM );
             $rec_count = $row[0];
             
             if( isset($_GET{'page'} ) )
             {
                $page = $_GET{'page'} + 1;
                $offset = $rec_limit * $page ;
             }
             else
             {
                $page = 0;
                $offset = 0;
             }
             $left_rec = $rec_count - ($page * $rec_limit);
             $sql = "SELECT emp_id, emp_name, emp_salary ".
                "FROM employee ".
                "LIMIT $offset, $rec_limit";
                
             $retval = mysql_query( $sql, $conn );
             
             if(! $retval )
             {
                die('Could not get data: ' . mysql_error());
             }
             
             while($row = mysql_fetch_array($retval, MYSQL_ASSOC))
             {
                echo "EMP ID :{$row['emp_id']}  <br> ".
                   "EMP NAME : {$row['emp_name']} <br> ".
                   EMP SALARY : {$row['emp_salary']} <br> ".
                   "--------------------------------<br>";
             }
             
             if( $page > 0 )
             {
                $last = $page - 2;
                echo "<a href=\"$_PHP_SELF?page=$last\">Last 10 Records</a> |";
                echo "<a href=\"$_PHP_SELF?page=$page\">Next 10 Records</a>";
             }
             
             else if( $page == 0 )
             {
                echo "<a href=\"$_PHP_SELF?page=$page\">Next 10 Records</a>";
    			}
    			
             else if( $left_rec < $rec_limit )
             {
                $last = $page - 2;
                echo "<a href=\"$_PHP_SELF?page=$last\">Last 10 Records</a>";
             }
             
             mysql_close($conn);
          ?>
          
       </body>
    </html>
    
  7. Updating Data into MySQL Database

    Data can be updated into MySQL tables by executing SQL UPDATE statement through PHP function mysql_query.

    Below is a simple example to update records into employee table. To update a record in any table it is required to locate that record by using a conditional clause. Below example uses primary key to match a record in employee table.

    Example:

    Try out following example to understand update operation. You need to provide an employee ID to update an employee salary.

    <html>
       
       <head>
          <title>Update a Record in MySQL Database</title>
       </head>
       
       <body>
          <?php
             if(isset($_POST['update']))
             {
                $dbhost = 'localhost:3036';
                $dbuser = 'root';
                $dbpass = 'rootpassword';
                
                $conn = mysql_connect($dbhost, $dbuser, $dbpass);
                
                if(! $conn )
                {
                   die('Could not connect: ' . mysql_error());
                }
                
                $emp_id = $_POST['emp_id'];
                $emp_salary = $_POST['emp_salary'];
                
                $sql = "UPDATE employee ". "SET emp_salary = $emp_salary ". "WHERE emp_id = $emp_id" ;
                mysql_select_db('test_db');
                $retval = mysql_query( $sql, $conn );
                
                if(! $retval )
                {
                   die('Could not update data: ' . mysql_error());
                }
                echo "Updated data successfully\n";
                
                mysql_close($conn);
             }
             else
             {
                ?>
                   <form method="post" action="<?php $_PHP_SELF ?>">
                      <table width="400" border="0" cellspacing="1" cellpadding="2">
                      
                         <tr>
                            <td width="100">Employee ID</td>
                            <td><input name="emp_id" type="text" id="emp_id"></td>
                         </tr>
                      
                         <tr>
                            <td width="100">Employee Salary</td>
                            <td><input name="emp_salary" type="text" id="emp_salary"></td>
                         </tr>
                      
                         <tr>
                            <td width="100"> </td>
                            <td> </td>
                         </tr>
                      
                         <tr>
                            <td width="100"> </td>
                            <td>
                               <input name="update" type="submit" id="update" value="Update">
                            </td>
                         </tr>
                      
                      </table>
                   </form>
                <?php
             }
          ?>
       </body>
    </html>
    
  8. Deleting Data from MySQL Database

    Data can be deleted from MySQL tables by executing SQL DELETE statement through PHP function mysql_query.

    Below is a simple example to delete records into employee table. To delete a record in any table it is required to locate that record by using a conditional clause. Below example uses primary key to match a record in employee table.

    Example:

    Try out following example to understand delete operation. You need to provide an employee ID to delete an employee record from employee table.

    <html>
       
       <head>
          <title>Delete a Record from MySQL Database</title>
       </head>
       
       <body>
          <?php
             if(isset($_POST['delete']))
             {
                $dbhost = 'localhost:3036';
                $dbuser = 'root';
                $dbpass = 'rootpassword';
                $conn = mysql_connect($dbhost, $dbuser, $dbpass);
                
                if(! $conn )
                {
                   die('Could not connect: ' . mysql_error());
                }
    				
                $emp_id = $_POST['emp_id'];
                
                $sql = "DELETE employee ". "WHERE emp_id = $emp_id" ;
                mysql_select_db('test_db');
                $retval = mysql_query( $sql, $conn );
                
                if(! $retval )
                {
                   die('Could not delete data: ' . mysql_error());
                }
                
                echo "Deleted data successfully\n";
                
                mysql_close($conn);
             }
             else
             {
                ?>
                   <form method="post" action="<?php $_PHP_SELF ?>">
                      <table width="400" border="0" cellspacing="1" cellpadding="2">
                         
                         <tr>
                            <td width="100">Employee ID</td>
                            <td><input name="emp_id" type="text" id="emp_id"></td>
                         </tr>
                         
                         <tr>
                            <td width="100"> </td>
                            <td> </td>
                         </tr>
                         
                         <tr>
                            <td width="100"> </td>
                            <td>
                               <input name="delete" type="submit" id="delete" value="Delete">
                            </td>
                         </tr>
                         
                      </table>
                   </form>
                <?php
             }
          ?>
          
       </body>
    </html>
    
  9. Perform MySQL backup using PHP

    It is always good practice to take a regular backup of your database. There are three ways you can use to take backup of your MySQL database.

    1. Using SQL Command through PHP.
    2. Using MySQL binary mysqldump through PHP.
    3. Using phpMyAdmin user interface.

    Using SQL Command through PHP

    You can execute SQL SELECT command to take a backup of any table. To take a complete database dump you will need to write separate query for separate table. Each table will be stored into separate text file.

    Example:

    Try out following example of using SELECT INTO OUTFILE query for creating table backup.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
    	
       $table_name = "employee";
       $backup_file  = "/tmp/employee.sql";
       $sql = "SELECT * INTO OUTFILE '$backup_file' FROM $table_name";
       
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not take data backup: ' . mysql_error());
       }
       
       echo "Backedup  data successfully\n";
       
       mysql_close($conn);
    ?>
    

    There may be instances when you would need to restore data which you have backed up some time ago. To restore the backup you just need to run LOAD DATA INFILE query like this:

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $conn = mysql_connect($dbhost, $dbuser, $dbpass);
       
       if(! $conn )
       {
          die('Could not connect: ' . mysql_error());
       }
    	
       $table_name = "employee";
       $backup_file  = "/tmp/employee.sql";
       $sql = "LOAD DATA INFILE '$backup_file' INTO TABLE $table_name";
       
       mysql_select_db('test_db');
       $retval = mysql_query( $sql, $conn );
       
       if(! $retval )
       {
          die('Could not load data : ' . mysql_error());
       }
       echo "Loaded  data successfully\n";
       
       mysql_close($conn);
    ?>
    

    Using MySQL binary mysqldump through PHP

    MySQL provides one utility mysqldump to perform database backup. Using this binary you can take complete database dump in a single command.

    Example:

    Try out following example to take your complete database dump.

    <?php
       $dbhost = 'localhost:3036';
       $dbuser = 'root';
       $dbpass = 'rootpassword';
       
       $backup_file = $dbname . date("Y-m-d-H-i-s") . '.gz';
       $command = "mysqldump --opt -h $dbhost -u $dbuser -p $dbpass ". "test_db | gzip > $backup_file";
       
       system($command);
    ?>
    

    Using phpMyAdmin user interface

    If you have phpMyAdmin user interface available then its very easy for your to take backup of your database.

    To backup your MySQL database using phpMyAdmin click on the "export" link on phpMyAdmin main page. Choose the database you wish to backup, check the appropriate SQL options and enter the name for the backup file.

What is AJAX ?

  1. AJAX stands for Asynchronous JavaScript and XML. AJAX is a new technique for creating better, faster, and more interactive web applications with the help of XML, HTML, CSS and Java Script.
  2. Conventional web application transmit information to and from the sever using synchronous requests. This means you fill out a form, hit submit, and get directed to a new page with new information from the server.
  3. With AJAX when submit is pressed, JavaScript will make a request to the server, interpret the results and update the current screen. In the purest sense, the user would never know that anything was even transmitted to the server.
  4. With AJAX, when you hit submit, JavaScript will make a request to the server, interpret the results, and update the current screen. In the purest sense, the user would never know that anything was even transmitted to the server.
  5. XML is commonly used as the format for receiving server data, although any format, including plain text, can be used.
  6. AJAX is a web browser technology independent of web server software.
  7. Intuitive and natural user interaction. Clicking is not required, mouse movement is a sufficient event trigger.
  8. Data-driven as opposed to page-driven.

Rich Internet Application Technology

AJAX is the most viable Rich Internet Application (RIA) technology so far. It is getting tremendous industry momentum and several tool kit and frameworks are emerging. But at the same time, AJAX has browser incompatibility and it is supported by JavaScript, which is hard to maintain and debug.

AJAX is Based on Open Standards

AJAX is based on the following open standards:

  1. Browser-based presentation using HTML and Cascading Style Sheets (CSS).
  2. Data is stored in XML format and fetched from the server.
  3. Behind-the-scenes data fetches using XMLHttpRequest objects in the browser.
  4. JavaScript to make everything happen.

AJAX - Technologies

AJAX cannot work independently. It is used in combination with other technologies to create interactive webpages.

JavaScript

  1. Loosely typed scripting language.
  2. JavaScript function is called when an event occurs in a page.
  3. Glue for the whole AJAX operation.

DOM

  1. API for accessing and manipulating structured documents.
  2. Represents the structure of XML and HTML documents.

CSS

  1. Allows for a clear separation of the presentation style from the content and may be changed programmatically by JavaScript.

XMLHttpRequest

  1. JavaScript object that performs asynchronous interaction with the server.

AJAX - Examples

Here is a list of some famous web applications that make use of AJAX

Google Maps

A user can drag an entire map by using the mouse, rather than clicking on a button.
http://maps.google.com/

Google Suggest

As you type, Google will offer suggestions. Use the arrow keys to navigate the results.
http://www.google.com/webhp?complete=1&hl=en

Gmail

Gmail is a webmail, built on the idea that email can be more intuitive, efficient and useful.
http://gmail.com/

Yahoo Maps (new)

Now it's even easier and more fun to get where you're going!
http://maps.yahoo.com/

Difference in AJAX and Conventional CGI Program

AJAX - Browser Support

All the available browsers cannot support AJAX. Here is a list of major browsers, that support AJAX.

  1. Mozilla Firefox 1.0 and above.
  2. Netscape version 7.1 and above.
  3. Apple Safari 1.2 and above.
  4. Microsoft Internet Explorer 5 and above.
  5. Konqueror.
  6. Opera 7.6 and above.

When you write your next application, do consider the browsers that do not support AJAX.

NOTE: When we say that a browser does not support AJAX, it simply means that the browser does not support creation of Javascript object XMLHttpRequest object.

Writing Browser Specific Code

The Simplest way to make your source code compatible with a browser is to use try...catch blocks in your JavaScript.

<html>
<body>
   <script language="javascript" type="text/javascript">
   <!-- 
   //Browser Support Code
   function ajaxFunction(){
      var ajaxRequest;  // The variable that makes Ajax possible!

      try{
         // Opera 8.0+, Firefox, Safari 
         ajaxRequest = new XMLHttpRequest();
      }catch (e){

         // Internet Explorer Browsers
         try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
         }catch (e) {
            try{
               ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            }catch (e){

               // Something went wrong
               alert("Your browser broke!");
               return false;
            }
         }
      }
   }
   //-->
   </script>
   
   <form name='myForm'>
      Name: <input type='text' name='username' /> <br />
      Time: <input type='text' name='time' />
   </form>
   
</body>
</html>

In the above JavaScript code, we try three times to make our XMLHttpRequest object. Our first attempt:

  1. ajaxRequest = new XMLHttpRequest();

It is for Opera 8.0+, Firefox, and Safari browsers. If it fails, we try two more times to make the correct object for an Internet Explorer browser with:

  1. ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
  2. ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");

If it doesn't work, then we can use a very outdated browser that doesn't support XMLHttpRequest, which also means it doesn't support Ajax.

Most likely though, our variable ajaxRequest will now be set to whatever XMLHttpRequest standard the browser uses and we can start sending data to the server. The step-wise AJAX workflow is explained in the next chapter.

AJAX - Action

A clear picture of the exact steps of AJAX operation.

Steps of AJAX Operation:

  1. A client event occurs
  2. An XMLHttpRequest object is created.
  3. The XMLHttpRequest object is configured.
  4. The XMLHttpRequest object makes an asynchronous request to the Webserver.
  5. The Webserver returns the result containing XML document.
  6. The XMLHttpRequest object calls the callback() function and processes the result.
  7. The HTML DOM is updated.

Let us take these steps one by one.

  1. A client event occurs

    1. A JavaScript function is called as the result of an event.
    2. Example: validateUserId() JavaScript function is mapped as an event handler to an onkeyup event on input form field whose id is set to "userid"
    3. <input type="text" size="20" id="userid" name="id" onkeyup="validateUserId();">.
  2. The XMLHttpRequest Object is Created

    var ajaxRequest;  // The variable that makes Ajax possible!
    function ajaxFunction(){
       try{
          
          // Opera 8.0+, Firefox, Safari
          ajaxRequest = new XMLHttpRequest();
       }catch (e){
       
          // Internet Explorer Browsers
          try{
             ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
          }catch (e) {
          
             try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
             }catch (e){
          
                // Something went wrong
                alert("Your browser broke!");
                return false;
             }
          }
       }
    }
    
  3. The XMLHttpRequest Object is Configured

    In this step, we will write a function that will be triggered by the client event and a callback function processRequest() will be registered.

    function validateUserId() {
       ajaxFunction();
       
       // Here processRequest() is the callback function.
       ajaxRequest.onreadystatechange = processRequest;
       
       if (!target) target = document.getElementById("userid");
       var url = "validate?id=" + escape(target.value);
       
       ajaxRequest.open("GET", url, true);
       ajaxRequest.send(null);
    }
    
  4. Making Asynchronous Request to the Webserver

    Source code is available in the above piece of code. Code written in bold typeface is responsible to make a request to the webserver. This is all being done using the XMLHttpRequest object ajaxRequest.

    function validateUserId() {
       ajaxFunction();
       
       // Here processRequest() is the callback function.
       ajaxRequest.onreadystatechange = processRequest;
       
       if (!target) target = document.getElementById("userid");
       var url = "validate?id=" + escape(target.value);
       
       ajaxRequest.open("GET", url, true);
       ajaxRequest.send(null);
    }
    

    Assume you enter Zara in the userid box, then in the above request, the URL is set to "validate?id=Zara".

  5. Webserver Returns the Result Containing XML Document

    You can implement your server-side script in any language, however its logic should be as follows.

    1. Get a request from the client.
    2. Parse the input from the client.
    3. Do required processing.
    4. Send the output to the client.

    If we assume that you are going to write a servlet, then here is the piece of code.

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException 
    {
       String targetId = request.getParameter("id");
       
       if ((targetId != null) && !accounts.containsKey(targetId.trim()))
       {
          response.setContentType("text/xml");
          response.setHeader("Cache-Control", "no-cache");
          response.getWriter().write("true");
       }
       else
       {
          response.setContentType("text/xml");
          response.setHeader("Cache-Control", "no-cache");
          response.getWriter().write("false");
       }
    }
    
  6. Callback Function processRequest() is Called

    The XMLHttpRequest object was configured to call the processRequest() function when there is a state change to the readyState of the XMLHttpRequest object. Now this function will receive the result from the server and will do the required processing. As in the following example, it sets a variable message on true or false based on the returned value from the Webserver.

     
    function processRequest() {
       if (req.readyState == 4) {
          if (req.status == 200) {
             var message = ...;
    ...
    }
    
  7. The HTML DOM is Updated

    This is the final step and in this step, your HTML page will be updated. It happens in the following way:

    1. JavaScript gets a reference to any element in a page using DOM API.
    2. The recommended way to gain a reference to an element is to call.
      document.getElementById("userIdMessage"), 
      // where "userIdMessage" is the ID attribute 
      // of an element appearing in the HTML document
      
    3. JavaScript may now be used to modify the element's attributes; modify the element's style properties; or add, remove, or modify the child elements. Here is an example:
      <script type="text/javascript">
      <!--
      function setMessageUsingDOM(message) {
         var userMessageElement = document.getElementById("userIdMessage");
         var messageText;
         
         if (message == "false") {
            userMessageElement.style.color = "red";
            messageText = "Invalid User Id";
         }
         else 
         {
            userMessageElement.style.color = "green";
            messageText = "Valid User Id";
         }
         
         var messageBody = document.createTextNode(messageText);
         
         // if the messageBody element has been created simple 
         // replace it otherwise append the new element
         if (userMessageElement.childNodes[0]) {
            userMessageElement.replaceChild(messageBody, userMessageElement.childNodes[0]);
         } 
         else
         {
            userMessageElement.appendChild(messageBody);
         }
      }
      -->
      </script>
      <body>
      <div id="userIdMessage"><div>
      </body>
      
  8. AJAX - XMLHttpRequest

    The XMLHttpRequest object is the key to AJAX. It has been available ever since Internet Explorer 5.5 was released in July 2000, but was not fully discovered until AJAX and Web 2.0 in 2005 became popular.

    XMLHttpRequest (XHR) is an API that can be used by JavaScript, JScript, VBScript, and other web browser scripting languages to transfer and manipulate XML data to and from a webserver using HTTP, establishing an independent connection channel between a webpage's Client-Side and Server-Side.

    The data returned from XMLHttpRequest calls will often be provided by back-end databases. Besides XML, XMLHttpRequest can be used to fetch data in other formats, e.g. JSON or even plain text.

    You already have seen a couple of examples on how to create an XMLHttpRequest object.

    Listed below is listed are some of the methods and properties that you have to get familiar with.

    XMLHttpRequest Methods

    1. abort()

      Cancels the current request.

    2. getAllResponseHeaders()

      Returns the complete set of HTTP headers as a string.

    3. getResponseHeader( headerName )

      Returns the value of the specified HTTP header.

    4. open( method, URL ) open( method, URL, async ) open( method, URL, async, userName ) open( method, URL, async, userName, password )

      Specifies the method, URL, and other optional attributes of a request.

      The method parameter can have a value of "GET", "POST", or "HEAD". Other HTTP methods, such as "PUT" and "DELETE" (primarily used in REST applications) may be possible.

      The "async" parameter specifies whether the request should be handled asynchronously or not. "true" means that the script processing carries on after the send() method without waiting for a response, and "false" means that the script waits for a response before continuing script processing.

    5. send( content )

      Sends the request.

    6. setRequestHeader( label, value )
    7. Adds a label/value pair to the HTTP header to be sent.

    XMLHttpRequest Properties

    1. onreadystatechange

      An event handler for an event that fires at every state change.

    2. readyState

      The readyState property defines the current state of the XMLHttpRequest object.

      The following table provides a list of the possible values for the readyState property:

      State Description
      0 The request is not initialized.
      1 The request has been set up.
      2 The request has been sent.
      3 The request is in process.
      4 The request is completed.

      readyState = 0 After you have created the XMLHttpRequest object, but before you have called the open() method.

      readyState = 1 After you have called the open() method, but before you have called send().

      readyState = 2 After you have called send().

      readyState = 3 After the browser has established a communication with the server, but before the server has completed the response.

      readyState = 4 After the request has been completed, and the response data has been completely received from the server.

    3. responseText

      Returns the response as a string.

    4. responseXML

      Returns the response as XML. This property returns an XML document object, which can be examined and parsed using the W3C DOM node tree methods and properties.

    5. status

      Returns the status as a number (e.g., 404 for "Not Found" and 200 for "OK").

    6. statusText

      Returns the status as a string (e.g., "Not Found" or "OK").

    AJAX - Database Operations

    To clearly illustrate how easy it is to access information from a database using AJAX, we are going to build MySQL queries on the fly and display the results on "ajax.html". But before we proceed, let us do the ground work. Create a table using the following command.

    NOTE: We are assuming you have sufficient privilege to perform the following MySQL operations

    CREATE TABLE 'ajax_example' (
       'name' varchar(50) NOT NULL,
       'age' int(11) NOT NULL,
       'sex' varchar(1) NOT NULL,
       'wpm' int(11) NOT NULL,
       PRIMARY KEY  ('name')
    ) 
    

    Now dump the following data into this table using the following SQL statements:

    INSERT INTO 'ajax_example' VALUES ('Jerry', 120, 'm', 20);
    INSERT INTO 'ajax_example' VALUES ('Regis', 75, 'm', 44);
    INSERT INTO 'ajax_example' VALUES ('Frank', 45, 'm', 87);
    INSERT INTO 'ajax_example' VALUES ('Jill', 22, 'f', 72);
    INSERT INTO 'ajax_example' VALUES ('Tracy', 27, 'f', 0);
    INSERT INTO 'ajax_example' VALUES ('Julie', 35, 'f', 90);
    

    Client Side HTML File

    Now let us have our client side HTML file, which is ajax.html, and it will have the following code:

    <html>
    <body>
    <script language="javascript" type="text/javascript">
    <!-- 
    //Browser Support Code
    function ajaxFunction(){
       var ajaxRequest;  // The variable that makes Ajax possible!
       try{
       
          // Opera 8.0+, Firefox, Safari
          ajaxRequest = new XMLHttpRequest();
       }catch (e){
          
          // Internet Explorer Browsers
          try{
             ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
          }catch (e) {
             
             try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
             }catch (e){
             
                // Something went wrong
                alert("Your browser broke!");
                return false;
             }
          }
       }
       
       // Create a function that will receive data
       // sent from the server and will update
       // div section in the same page.
       ajaxRequest.onreadystatechange = function(){
       
          if(ajaxRequest.readyState == 4){
             var ajaxDisplay = document.getElementById('ajaxDiv');
             ajaxDisplay.innerHTML = ajaxRequest.responseText;
          }
       }
       
       // Now get the value from user and pass it to
       // server script.
       var age = document.getElementById('age').value;
       var wpm = document.getElementById('wpm').value;
       var sex = document.getElementById('sex').value;
       var queryString = "?age=" + age ;
       
       queryString +=  "&wpm=" + wpm + "&sex=" + sex;
       ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
       ajaxRequest.send(null); 
    }
    //-->
    </script>
    
    <form name='myForm'>
    
       Max Age: <input type='text' id='age' /> <br />
       Max WPM: <input type='text' id='wpm' /> <br />
       Sex: 
       <select id='sex'>
          <option value="m">m</option>
          <option value="f">f</option>
       </select>
       <input type='button' onclick='ajaxFunction()' value='Query MySQL'/>
       
    </form>
    <div id='ajaxDiv'>Your result will display here</div>
    </body>
    </html>
    

    NOTE: The way of passing variables in the Query is according to HTTP standard and have formA.

    URL?variable1=value1;&variable2=value2;

    Server Side PHP File

    Your client-side script is ready. Now, we have to write our server-side script, which will fetch age, wpm, and sex from the database and will send it back to the client. Put the following code into the file "ajax-example.php".

    <?php
    $dbhost = "localhost";
    $dbuser = "dbusername";
    $dbpass = "dbpassword";
    $dbname = "dbname";
    	
    //Connect to MySQL Server
    mysql_connect($dbhost, $dbuser, $dbpass);
    	
    //Select Database
    mysql_select_db($dbname) or die(mysql_error());
    	
    // Retrieve data from Query String
    $age = $_GET['age'];
    $sex = $_GET['sex'];
    $wpm = $_GET['wpm'];
    	
    // Escape User Input to help prevent SQL Injection
    $age = mysql_real_escape_string($age);
    $sex = mysql_real_escape_string($sex);
    $wpm = mysql_real_escape_string($wpm);
    	
    //build query
    $query = "SELECT * FROM ajax_example WHERE sex = '$sex'";
    
    if(is_numeric($age))
       $query .= " AND age <= $age";
    
    if(is_numeric($wpm))
       $query .= " AND wpm <= $wpm";
    	
    //Execute query
    $qry_result = mysql_query($query) or die(mysql_error());
    
    //Build Result String
    $display_string = "<table>";
    $display_string .= "<tr>";
    $display_string .= "<th>Name</th>";
    $display_string .= "<th>Age</th>";
    $display_string .= "<th>Sex</th>";
    $display_string .= "<th>WPM</th>";
    $display_string .= "</tr>";
    
    // Insert a new row in the table for each person returned
    while($row = mysql_fetch_array($qry_result)){
       $display_string .= "<tr>";
       $display_string .= "<td>$row[name]</td>";
       $display_string .= "<td>$row[age]</td>";
       $display_string .= "<td>$row[sex]</td>";
       $display_string .= "<td>$row[wpm]</td>";
       $display_string .= "</tr>";
    }
    
    echo "Query: " . $query . "<br />";
    $display_string .= "</table>";
    
    echo $display_string;
    ?>
    

    AJAX - Security

    AJAX Security: Server Side

    1. AJAX-based Web applications use the same server-side security schemes of regular Web applications.
    2. You specify authentication, authorization, and data protection requirements in your web.xml file (declarative) or in your program (programmatic).
    3. AJAX-based Web applications are subject to the same security threats as regular Web applications.

    AJAX Security: Client Side

    1. JavaScript code is visible to a user/hacker. Hacker can use JavaScript code for inferring server-side weaknesses.
    2. JavaScript code is downloaded from the server and executed ("eval") at the client and can compromise the client by mal-intended code.
    3. Downloaded JavaScript code is constrained by the sand-box security model and can be relaxed for signed JavaScript.

    AJAX - Issues

    AJAX is growing very fast and that is the reason that it contains many issues with it. We hope with the passes of time, they will be resolved and AJAX will become ideal for web applications. We are listing down a few issues that AJAX currently suffers from.

    Complexity is increased

    1. Server-side developers will need to understand that presentation logic will be required in the HTML client pages as well as in the server-side logic.
    2. Page developers must have JavaScript technology skills.

    AJAX-based applications can be difficult to debug, test, and maintain

    1. JavaScript is hard to test - automatic testing is hard.
    2. Weak modularity in JavaScript.
    3. Lack of design patterns or best practice guidelines yet.

    Toolkits/Frameworks are not mature yet

    1. Most of them are in beta phase.

    No standardization of the XMLHttpRequest yet

    1. Future version of IE will address this.

    No support of XMLHttpRequest in old browsers

    1. Iframe will help.

    JavaScript technology dependency and incompatibility

    1. Must be enabled for applications to function.
    2. Still some browser incompatibilities exist.

    JavaScript code is visible to a hacker

    1. Poorly designed JavaScript code can invite security problems.

XML is a markup language that looks a lot like HTML. An XML document is plain text and contains tags delimited by < and >. There are two big differences between XML and HTML:

  1. XML doesn't define a specific set of tags you must use.
  2. XML is extremely picky about document structure.

XML gives you a lot more freedom than HTML. HTML has a certain set of tags: the <a></a> tags surround a link, the <p> starts paragraph and so on. An XML document, however, can use any tags you want. Put tags around a movie rating, <height></height> tags around someone's height. Thus XML gives you option to define your own tags.

XML is very strict when it comes to document structure. HTML lets you play fast and loose with some opening and closing tags. But this is not the case with XML.

HTML list that's not valid XML

<ul>
   <li>Braised Sea Cucumber
   <li>Baked Giblets with Salt
   <li>Abalone with Marrow and Duck Feet
</ul>

This is not a valid XML document because there are no closing tags to match up with the three opening <li> tags. Every opened tag in an XML document must be closed.

HTML list that is valid XML

<ul>
   <li>Braised Sea Cucumber</li>
   <li>Baked Giblets with Salt</li>
  <li>Abalone with Marrow and Duck Feet</li>
</ul>

Parsing an XML Document

PHP 5's new SimpleXML module makes parsing an XML document, well, simple. It turns an XML document into an object that provides structured access to the XML.

To create a SimpleXML object from an XML document stored in a string, pass the string to simplexml_load_string( ). It returns a SimpleXML object.

Example:

Try out following example.

<html>
   <body>
      
      <?php
         $note=<<<XML
         
         <note>
            <to>Gopal K Verma</to>
            <from>Sairamkrishna</from>
            <heading>Project submission</heading>
            <body>Please see clearly </body>
         </note>
         
         XML;
         $xml=simplexml_load_string($note);
         print_r($xml);
      ?>
		
   </body>
</html>

It will produce the following result:

SimpleXMLElement Object ( [to] => Gopal K Verma [from] => Sairamkrishna [heading] => 
Project submission [body] => Please see clearly ) 

NOTE − You can use function simplexml_load_file( filename) if you have XML content in a file.

Generating an XML Document

SimpleXML is good for parsing existing XML documents, but you can't use it to create a new one from scratch.

The easiest way to generate an XML document is to build a PHP array whose structure mirrors that of the XML document and then to iterate through the array, printing each element with appropriate formatting.

Example:

Try out following example:

<?php
   $channel = array('title' => "What's For Dinner",
      'link' => 'http://menu.example.com/',
      'description' => 'Choose what to eat tonight.');
   
   print "\n";
   
   foreach ($channel as $element => $content) {
      print " <$element>";
      print htmlentities($content);
      print "\n";
   }
   
   print "";
?>

It will produce the following result:


   <title>What's For Dinner</title>
   <link>http://menu.example.com/</link>
   <description>Choose what to eat tonight.</description>
</channel>

We can imagine our universe made of different objects like sun, earth, moon etc. Similarly we can imagine our car made of different objects like wheel, steering, gear etc. Same way there is object oriented programming concepts which assume everything as an object and implement a software using different objects.

Object Oriented Concepts

Before we go in detail, lets define important terms related to Object Oriented Programming.

  1. Class: This is a programmer-defined data type, which includes local functions as well as local data. You can think of a class as a template for making many instances of the same kind (or class) of object.
  2. Object: An individual instance of the data structure defined by a class. You define a class once and then make many objects that belong to it. Objects are also known as instance.
  3. Member Variable: These are the variables defined inside a class. This data will be invisible to the outside of the class and can be accessed via member functions. These variables are called attribute of the object once an object is created.
  4. Member function: These are the function defined inside a class and are used to access object data.
  5. Inheritance: When a class is defined by inheriting existing function of a parent class then it is called inheritance. Here child class will inherit all or few member functions and variables of a parent class.
  6. Parent class: A class that is inherited from by another class. This is also called a base class or super class.
  7. Child Class: A class that inherits from another class. This is also called a subclass or derived class.
  8. Polymorphism: This is an object oriented concept where same function can be used for different purposes. For example function name will remain same but it make take different number of arguments and can do different task.
  9. Overloading: A type of polymorphism in which some or all of operators have different implementations depending on the types of their arguments. Similarly functions can also be overloaded with different implementation.
  10. Data Abstraction: Any representation of data in which the implementation details are hidden (abstracted).
  11. Encapsulation: Refers to a concept where we encapsulate all the data and member functions together to form an object.
  12. Constructor: Refers to a special type of function which will be called automatically whenever there is an object formation from a class.
  13. Destructor: Refers to a special type of function which will be called automatically whenever an object is deleted or goes out of scope.

Defining PHP Classes

The general form for defining a new class in PHP is as follows:

<?php
   class phpClass{
      var $var1;
      var $var2 = "constant string";
      
      function myfunc ($arg1, $arg2) {
         [..]
      }
      [..]
   }
?>

Here is the description of each line:

  1. The special form class, followed by the name of the class that you want to define.
  2. A set of braces enclosing any number of variable declarations and function definitions.
  3. Variable declarations start with the special form var, which is followed by a conventional $ variable name; they may also have an initial assignment to a constant value.
  4. Function definitions look much like standalone PHP functions but are local to the class and will be used to set and access object data.

Example:

Here is an example which defines a class of Books type.

<?php
   class  Books{
      /* Member variables */
      var $price;
      var $title;
      
      /* Member functions */
      function setPrice($par){
         $this->price = $par;
      }
      
      function getPrice(){
         echo $this->price ."<br/>";
      }
      
      function setTitle($par){
         $this->title = $par;
      }
      
      function getTitle(){
         echo $this->title ." <br/>";
      }
   }
?>

The variable $this is a special variable and it refers to the same object ie. itself.

Creating Objects in PHP

Once you defined your class, then you can create as many objects as you like of that class type. Following is an example of how to create object using new operator.

$physics = new Books;
$maths = new Books;
$chemistry = new Books;

Here we have created three objects and these objects are independent of each other and they will have their existence separately. Next we will see how to access member function and process member variables.

Calling Member Functions

After creating your objects, you will be able to call member functions related to that object. One member function will be able to process member variable of related object only.

Following example shows how to set title and prices for the three books by calling member functions.

$physics->setTitle( "Physics for High School" );
$chemistry->setTitle( "Advanced Chemistry" );
$maths->setTitle( "Algebra" );

$physics->setPrice( 10 );
$chemistry->setPrice( 15 );
$maths->setPrice( 7 );

Now you call another member functions to get the values set by in above example.

$physics->getTitle();
$chemistry->getTitle();
$maths->getTitle();
$physics->getPrice();
$chemistry->getPrice();
$maths->getPrice();

This will produce the following result:

Physics for High School
Advanced Chemistry
Algebra
10
15
7

Constructor Functions

Constructor Functions are special type of functions which are called automatically whenever an object is created. So we take full advantage of this behaviour, by initializing many things through constructor functions.

PHP provides a special function called __construct() to define a constructor. You can pass as many as arguments you like into the constructor function.

Following example will create one constructor for Books class and it will initialize price and title for the book at the time of object creation.

function __construct( $par1, $par2 ){
   $this->price = $par1;
   $this->title = $par2;
}

Now we don't need to call set function separately to set price and title. We can initialize these two member variables at the time of object creation only. Check following example below:

$physics = new Books( "Physics for High School", 10 );
$maths = new Books ( "Advanced Chemistry", 15 );
$chemistry = new Books ("Algebra", 7 );

/* Get those set values */
$physics->getTitle();
$chemistry->getTitle();
$maths->getTitle();

$physics->getPrice();
$chemistry->getPrice();
$maths->getPrice();

This will produce the following result:

Physics for High School
Advanced Chemistry
Algebra
10
15
7

Destructor

Like a constructor function you can define a destructor function using function __destruct(). You can release all the resources with-in a destructor.

Inheritance

PHP class definitions can optionally inherit from a parent class definition by using the extends clause. The syntax is as follows:

class Child extends Parent {
   
}

The effect of inheritance is that the child class (or subclass or derived class) has the following characteristics

  1. Automatically has all the member variable declarations of the parent class.
  2. Automatically has all the same member functions as the parent, which (by default) will work the same way as those functions do in the parent.

Following example inherit Books class and adds more functionality based on the requirement.

class Novel extends Books{
   var publisher;
   
   function setPublisher($par){
      $this->publisher = $par;
   }
   
   function getPublisher(){
      echo $this->publisher. "<br />";
   }
}

Now apart from inherited functions, class Novel keeps two additional member functions.

Function Overriding

Function definitions in child classes override definitions with the same name in parent classes. In a child class, we can modify the definition of a function inherited from parent class.

In the following example getPrice and getTitle functions are overridden to return some values.

function getPrice(){
   echo $this->price . "<br/>";
   return $this->price;
}
   
function getTitle(){
   echo $this->title . "<br/>";
   return $this->title;
}

Public Members

Unless you specify otherwise, properties and methods of a class are public. That is to say, they may be accessed in three possible situations:

  1. From outside the class in which it is declared
  2. From within the class in which it is declared
  3. From within another class that implements the class in which it is declared

Till now we have seen all members as public members. If you wish to limit the accessibility of the members of a class then you define class members as private or protected.

Private members

By designating a member private, you limit its accessibility to the class in which it is declared. The private member cannot be referred to from classes that inherit the class in which it is declared and cannot be accessed from outside the class.

A class member can be made private by using private keyword infront of the member.

class MyClass {
   private $car = "skoda";
   $driver = "SRK";
   
   function __construct($par) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }
   
   function myPublicFunction() {
      return("I'm visible!");
   }
   
   private function myPrivateFunction() {
      return("I'm  not visible outside!");
   }
}

When MyClass class is inherited by another class using extends, myPublicFunction() will be visible, as will $driver. The extending class will not have any awareness of or access to myPrivateFunction and $car, because they are declared private.

Protected members

A protected property or method is accessible in the class in which it is declared, as well as in classes that extend that class. Protected members are not available outside of those two kinds of classes. A class member can be made protected by using protected keyword in front of the member.

Here is different version of MyClass:

class MyClass {
   protected $car = "skoda";
   $driver = "SRK";

   function __construct($par) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }
   
   function myPublicFunction() {
      return("I'm visible!");
   }
   
   protected function myPrivateFunction() {
      return("I'm  visible in child class!");
   }
}

Interfaces

Interfaces are defined to provide a common function names to the implementers. Different implementors can implement those interfaces according to their requirements. You can say, interfaces are skeletons which are implemented by developers.

As of PHP5, it is possible to define an interface, like this:

interface Mail {
   public function sendMail();
}

Then, if another class implemented that interface, like this:

class Report implements Mail {
   // sendMail() Definition goes here
}

Constants

A constant is somewhat like a variable, in that it holds a value, but is really more like a function because a constant is immutable. Once you declare a constant, it does not change.

Declaring one constant is easy, as is done in this version of MyClass:

class MyClass {
   const requiredMargin = 1.7;
   
   function __construct($incomingValue) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }
}

In this class, requiredMargin is a constant. It is declared with the keyword const, and under no circumstances can it be changed to anything other than 1.7. Note that the constant's name does not have a leading $, as variable names do.

Abstract Classes

An abstract class is one that cannot be instantiated, only inherited. You declare an abstract class with the keyword abstract, like this:

When inheriting from an abstract class, all methods marked abstract in the parent's class declaration must be defined by the child; additionally, these methods must be defined with the same visibility.

abstract class MyAbstractClass {
   abstract function myAbstractFunction() {
   }
}

Note that function definitions inside an abstract class must also be preceded by the keyword abstract. It is not legal to have abstract function definitions inside a non-abstract class.

Static Keyword

Declaring class members or methods as static makes them accessible without needing an instantiation of the class. A member declared as static can not be accessed with an instantiated class object (though a static method can).

Try out following example:

<?php
   class Foo
   {
      public static $my_static = 'foo';
      
      public function staticValue() {
         return self::$my_static;
      }
   }
	
   print Foo::$my_static . "\n";
   $foo = new Foo();
   
   print $foo->staticValue() . "\n";
?>	

Final Keyword

PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.

Following example results in Fatal error: Cannot override final method BaseClass::moreTesting()

<?php

   class BaseClass {
      public function test() {
         echo "BaseClass::test() called<br>";
      }
      
      final public function moreTesting() {
         echo "BaseClass::moreTesting() called<br>";
      }
   }
   
   class ChildClass extends BaseClass {
      public function moreTesting() {
         echo "ChildClass::moreTesting() called<br>";
      }
   }
?>

Calling parent constructors

Instead of writing an entirely new constructor for the subclass, let's write it by calling the parent's constructor explicitly and then doing whatever is necessary in addition for instantiation of the subclass. Here's a simple example

class Name
{
   var $_firstName;
   var $_lastName;
   
   function Name($first_name, $last_name)
   {
      $this->_firstName = $first_name;
      $this->_lastName = $last_name;
   }
   
   function toString() {
      return($this->_lastName .", " .$this->_firstName);
   }
}
class NameSub1 extends Name
{
   var $_middleInitial;
   
   function NameSub1($first_name, $middle_initial, $last_name) {
      Name::Name($first_name, $last_name);
      $this->_middleInitial = $middle_initial;
   }
   
   function toString() {
      return(Name::toString() . " " . $this->_middleInitial);
   }
}

In this example, we have a parent class (Name), which has a two-argument constructor, and a subclass (NameSub1), which has a three-argument constructor. The constructor of NameSub1 functions by calling its parent constructor explicitly using the :: syntax (passing two of its arguments along) and then setting an additional field. Similarly, NameSub1 defines its non constructor toString() function in terms of the parent function that it overrides.

NOTE: A constructor can be defined with the same name as the name of a class. It is defined in above example.

The simplest way to think of PHP is as interpreted C that you can embed in HTML documents. The language itself is a lot like C, except with untyped variables, a whole lot of Web-specific libraries built in, and everything hooked up directly to your favorite Web server.

The syntax of statements and function definitions should be familiar, except that variables are always preceded by $, and functions do not require separate prototypes.

Here we will put some similarities and differences in PHP and C.

Similarities

  1. Syntax: Broadly speaking, PHP syntax is the same as in C: Code is blank insensitive, statements are terminated with semicolons, function calls have the same structure (my_function(expression1, expression2)), and curly braces ({ and }) make statements into blocks. PHP supports C and C++-style comments (/* */ as well as //), and also Perl and shell-script style (#).
  2. Operators: The assignment operators (=, +=, *=, and so on), the Boolean operators (&&, ||, !), the comparison operators (<,>, <=, >=, ==, !=), and the basic arithmetic operators (+, -, *, /, %) all behave in PHP as they do in C.
  3. Control structures: The basic control structures (if, switch, while, for) behave as they do in C, including supporting break and continue. One notable difference is that switch in PHP can accept strings as case identifiers.
  4. Function names: As you peruse the documentation, you.ll see many function names that seem identical to C functions.

Differences

  1. Dollar signs: All variables are denoted with a leading $. Variables do not need to be declared in advance of assignment, and they have no intrinsic type.
  2. Types: PHP has only two numerical types: integer (corresponding to a long in C) and double (corresponding to a double in C). Strings are of arbitrary length. There is no separate character type.
  3. Type conversion: Types are not checked at compile time, and type errors do not typically occur at runtime either. Instead, variables and values are automatically converted across types as needed.
  4. Arrays: Arrays have a syntax superficially similar to C's array syntax, but they are implemented completely differently. They are actually associative arrays or hashes, and the index can be either a number or a string. They do not need to be declared or allocated in advance.
  5. No structure type: There is no structure in PHP, partly because the array and object types together make it unnecessary. The elements of a PHP array need not be of a consistent type.
  6. No pointers: There are no pointers available in PHP, although the tapeless variables play a similar role. PHP does support variable references. You can also emulate function pointers to some extent, in that function names can be stored in variables and called by using the variable rather than a literal name.
  7. No prototypes: Functions do not need to be declared before their implementation is defined, as long as the definition can be found somewhere in the current code file or included files.
  8. Memory management: The PHP engine is effectively a garbage-collected environment (reference-counted), and in small scripts there is no need to do any deallocation. You should freely allocate new structures - such as new strings and object instances. IN PHP5, it is possible to define destructor for objects, but there is no free or delete. Destructor are called when the last reference to an object goes away, before the memory is reclaimed.
  9. Compilation and linking: There is no separate compilation step for PHP scripts.
  10. Permissiveness: As a general matter, PHP is more forgiving than C (especially in its type system) and so will let you get away with new kinds of mistakes. Unexpected results are more common than errors.

This chapter will list out major similarities and differences in between PHP and PERL. This will help PERL developers to understand PHP very quickly and avoid common mistakes.

Similarities

  1. Compiled scripting languages: Both Perl and PHP are scripting languages.This means that they are not used to produce native standalone executables in advance of execution.
  2. Syntax: PHP's basic syntax is very close to Perl's, and both share a lot of syntactic features with C. Code is insensitive to whitespace, statements are terminated by semicolons, and curly braces organize multiple statements into a single block. Function calls start with the name of the function, followed by the actual arguments enclosed in parentheses and separated by commas.
  3. Dollar-sign variables: All variables in PHP look like scalar variables in Perl: a name with a dollar sign ($) in front of it.
  4. No declaration of variables: As in Perl, you don.t need to declare the type of a PHP variable before using it.
  5. Loose typing of variables: As in Perl, variables in PHP have no intrinsic type other than the value they currently hold. You can store either number or string in same type of variable.
  6. Strings and variable interpolation: Both PHP and Perl do more interpretation of double-quoted strings ("string") than of singlequoted strings ('string').

Differences

  1. PHP is HTML-embedded: Although it is possible to use PHP for arbitrary tasks by running it from the command line, it is more typically connected to a Web server and used for producing Web pages. If you are used to writing CGI scripts in Perl, the main difference in PHP is that you no longer need to explicitly print large blocks of static HTML using print or heredoc statements and instead can simply write the HTML itself outside of the PHP code block.
  2. No @ or % variables: PHP has one only kind of variable, which starts with a dollar sign ($). Any of the datatypes in the language can be stored in such variables, whether scalar or compound.
  3. Arrays versus hashes: PHP has a single datatype called an array that plays the role of both hashes and arrays/lists in Perl.
  4. Specifying arguments to functions: Function calls in PHP look pretty much like subroutine calls in Perl. Function definitions in PHP, on the other hand, typically require some kind of list of formal arguments as in C or Java which is not the csse in PERL.
  5. Variable scoping in functions: In Perl, the default scope for variables is global. This means that top-level variables are visible inside subroutines. Often, this leads to promiscuous use of globals across functions. In PHP, the scope of variables within function definitions is local by default.
  6. No module system as such: In PHP there is no real distinction between normal code files and code files used as imported libraries.
  7. Break and continue rather than next and last: PHP is more like C langauge and uses break and continue instead of next and last statement.
  8. No elsif: A minor spelling difference: Perl's elsif is PHP's elseif.
  9. More kinds of comments: In addition to Perl-style (#) single-line comments, PHP offers C-style multiline comments (/* comment */ ) and Java-style single-line comments (// comment).
  10. Regular expressions: PHP does not have a built-in syntax specific to regular expressions, but has most of the same functionality in its "Perl-compatible" regular expression functions.