php language presentation
TRANSCRIPT
PHP• Amol Gharpure-13• Apurva Bharatiya-17• Annujj Agarwal-06• Nirmiti Dhurve-30
Background• Started as a Perl hack in 1994 by Rasmus Lerdorf (to handle his
resume), developed to PHP/FI 2.0• By 1997 up to PHP 3.0 with a new parser engine by Zeev Suraski and
Andi Gutmans• Version 5.2.4 is current version, rewritten by Zend (www.zend.com) to
include a number of features, such as an object model• Current is version 5• php is one of the premier examples of what an open source project
can be
Why PHP?• You can build dynamic pages with just the information in a php script• But where php shines is in building pages out of external data
sources, so that the web pages change when the data does• Most of the time, people think of a database like MySQL as the
backend, but you can also use text or other files, LDAP, pretty much anything….
INTRODUCTION• HYPERTEXT PREPROCESSOR (PHP) is a server side scripting language
that is embedded in HTML.• Used to manage dynamic content, databases, sessions tracking, even
built entire e-commerce site.• It is integrated with a number of popular databases, including MySQL,
Oracle, Microsoft SQL Server, etc.• Can also be used as general-purpose programming language.• PHP code can be simply mixed with HTML code, or it can be used in
combination with various templating engines and web frameworks.
Continued…• PHP code is usually processed by a PHP interpreter, which is usually
implemented as a web server’s native module.• After the PHP code is interpreted and executed, the web server sends
resulting output to its client, usually in form of a part of the generated web page; for example, PHP code can generate a web page’s HTML code, an image, or some other data.• PHP has also evolved to include a command-line interface(CLI)
capability and can be used in standalone graphical applications.
PHP Scripts• Typically file ends in .php--this is set by the web server configuration • Separated in files with the <?php ?> tag • php commands can make up an entire file, or can be contained in html--this is a choice….• Program lines end in ";" or you get an error• Server recognizes embedded script and executes• Result is passed to browser, source isn't visible• <P>• <?php $myvar = "Hello World!"; • echo $myvar;• ?>• </P>
Parsing• We've talk about how the browser can read a text file and process it,
that's a basic parsing method• Parsing involves acting on relevant portions of a file and ignoring
others• Browsers parse web pages as they load• Web servers with server side technologies like php parse web pages
as they are being passed out to the browser
Two Ways• You can embed sections of php inside html:<BODY><P><?php $myvar = "Hello World!"; echo $myvar;</BODY>
• Or you can call html from php:<?phpecho "<html><head><title>Howdy</title>…?>
How to run a PHP file?• PHP files first need to be processed in a web server before sending
their output to the web browser.• Therefore before running PHP files, they should be placed inside the
web folder of a web server and then make a request to desired PHP file by typing its URL in the web browser. If you installed a web server in your computer, usually the root of its web folder can be accessed by typing http://localhost in the web browser. So, if you placed a file called hello.php inside its web folder, you can run that file by calling http://localhost/hello.php.
Basic Syntax• Syntax based on Perl, Java, and C • The PHP parsing engine needs a way to differentiate PHP code from other elements. The
mechanism for doing so is known as ‘encapsing to PHP’’. There are four ways to do it:• Canonical PHP tags: <?php..?>• Short-Open(SGML-style) tags: <?....?>• ASP-style tags: <%...%>• HTML script tags:• <script language=“PHP”>…</script>
Comments• There are two commenting formats in PHP:1. Single-line comments2. Multi-line comments <? #This is a comment //So is this a comment /*This is the second line of comment This is a comment too*/ print ”An example with single line comments”; ?>
Continued(Basic Syntax)…• PHP is case sensitive.• For example <html> <body> <?$capital=67;print(“Variable capital is $capital<br>”);print(“Variable capiTal is $capiTal<br>”);?>Output:Variable capital is 67Variable capiTal is
Three-tiered Web Site: LAMPClientUser-agent: Firefox
ServerApache HTTP Server
example requestGET / HTTP/1.1Host: www.tamk.fiUser-Agent: Mozilla/5.0 (Mac..)...
response
DatabaseMySQL
PHP
Variables• Variables in PHP are represented by a dollar sign• PHP supports eight types:• boolean, integer, float, double, array, object, resource and NULL
Example (php.net)<?php
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer
echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
// If $bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
Naming Variables• Case-sensitivity• Start with letter or _• After that you can have numbers, letters and _• $var = 'Barney';• $Var = ‘MiaKhalifa';• print "$var, $Var"; • $4site = ‘Legendary'; • $_4site = ‘LAMP';
Constants• You cannot alter the value of constant after declaration• define(CONSTANT, "value");• print CONSTANT;
Example
<?php$a = “Paul ";print ”For " . $a;?>
<?php$a = “Batman";function Test() { print $a;}print ”Bruce Wayne is ”;Test();?>
Example
Control Structures• If, else, elseif, switch• while, do-while, for• foreach• break, continue•
Statements• Every statement ends with ;• $a = 5;• $a = function();• $a = ($b = 5);• $a++; ++$a;• $a += 3;
Operators• Arithmethic: +,-,*,%• Setting variable: =• Bit: &, |, ^, ~, <<, >>• Comparison: ==, ===, !=, !==, <, > <=, >=
Logical Operators• $a and $b• $a or $b• $a xor $b• !$a;• $a && $b;• $a || $b;
IF<?php
if ($a > $b) {
echo "a is bigger than b";
} else {
echo "a is NOT bigger than b";
}
if ($a > $b) {
echo "a is bigger than b";
} elseif ($a == $b) {
echo "a is equal to b";
} else {
echo "a is smaller than b";
}
?>
While and Do-While<?php$a=0;while($a<10){ print $a; $a++;}
$i = 0;do { print $i;} while ($i > 0);?>
For
for ($i = 1; $i <= 10; $i++) { print $i;}
Foreach$arr = array(1, 2, 3, 4);foreach ($arr as $value) { echo $value;}
Switchswitch ($i) {case 0: echo "i equals 0"; break;case 1: echo "i equals 1"; break;case 2: echo "i equals 2"; break;}
PHP COOKIES
What is a cookie?A cookie is a small text file that is stored on a user’s computer.Each cookie on the user’s computer is connected to a particular domain.Each cookie can be used to store upto 4kB of data.A maximum of 20 cookies can be stored on a user’s pc per domain.
Example(1)• User sends a request for page at www.example.com for the first time.
PAGE REQUEST
Example (2)• Server sends back the page xhtml to the browser AND stores some
data in a cookie on the user’s pc.
XHTML
COOKIE DATA
Example(1)• At the next page request for domain www.example.com, all the
cookie data associated with this domain is sent too.
Page request
Cookie data
Set a cookie• setcookie (name [,value [,expire [,path [,domain [,secure]]]]]) name = cookie namevalue = data to store (string)expire = UNIX timestamp when the cookie expires.Default is that cookie expires when the browser is closed.path = path on the server within and below which the cookie is available on.domain = domain at which the cookie is available on.secure = If cookie should be sent over HTTPS connection only. Default false.
Set a cookie-examples• setcookie (‘name’, ‘Robert’)• This command will set the cookie called name on the user’s PC
containing the data Robert. It will be available to all pages in the same directory or subdirectory of the page that set it(the default path and domain). It will expire and be deleted when the browser is closed (default expire).
Set a cookie-examples• setcookie (’age’, ‘20’, time () +60*60*24*30)• This command will set the cookie called age on the user’s PC
containing the data 20. It will be available to all pages in the same directory or subdirectory of the page that set it (the default path and domain). It will expire and be deleted after 30 days.
Set a cookie-examples• setcookie ( ‘gender’ , ’male’ , 0 , ’/’ )• This command will set the cookie called gender on the user’s PC
containing the data male. It will be available within the entire domain that set it. It will expire and be deleted when the browser is closed.
Read cookie data• All cookie data is available through the superglobal $_COOKIE:• $variable = $_COOKIE[‘cookie_name’]• OR• $variable = $HTTP_COOKIE_VARS[‘cookie_name’] ;e.g.$age = $_COOKIE[‘age’]
Storing an array..• Only strings can be stored in Cookie files.• To store an array in a cookie, convert it to a string by using the
serialize() PHP function.• The array can be reconstructed using the unserialize() function once it
had been read back in.• Remember cookie size is limited.
Delete a cookie• To remove a cookie, simply overwrite the cookie with a new one with
an expiry time in the past..
• setcookie (‘cookie_name’, ‘’, time () -6000)
• Note that theoretically any number taken away from the time() function should do, but due to variations in local computer times, it is advisable to use a day or two.
Malicious Cookie Usage• There is a bit of a stigma attached to cookies – and they can
be maliciously used (e.g. set via 3rd party banner ads).• The important thing is to note is that some people browse
with them turned off.
e.g. in FF, Tools>Options>Privacy
The USER is in control• Cookies are stored client-side, so never trust them completely: They
can be easily viewed, modified or created by a 3rd party.• They can be turned on and off at will by the user.
PHP WEB CONCEPTS
UserProfileServer
web serverweb serverWeb Server
ScriptsLoad Balancer
AdServer
Web Services
Apache
Server Architecture
Three-tiered Web Site: LAMPClientUser-agent: Firefox
ServerApache HTTP Server
example requestGET / HTTP/1.1Host: www.tamk.fiUser-Agent: Mozilla/5.0 (Mac..)...
response
DatabaseMySQL
PHP
Server Side Techniques• Server side scripting requires installation on the server side• Typically client siis only xhtml and it unaware that the xhtml was
produced by a server side script• Does not require any installations or add-ons on the client
Server Side Techniques• PHP• Java EE: Servlet, JSP• .NET• CGI / Perl (Very old)• Ruby• …
Client Side Techniques• Requires that the client supports the technique• JavaScript, Applet, Flash…
Web Application Frameworks• A web application framework is a software framework that is
designed to support the development of dynamic websites, Web applications and Web services.• Numerous frameworks available for many languages
Web App vs. Web Site?• What’s the difference between Web App and Web Site?• Rich Internet Application?, AJAX?, Thin Client?• Full application running in your browser or just a web site?
Server VariablesThe $_SERVER array variable is a reserved variable that contains all server information.
<html><head></head><body>
<?phpecho "Referer: " . $_SERVER["HTTP_REFERER"] . "<br />";echo "Browser: " . $_SERVER["HTTP_USER_AGENT"] . "<br />";echo "User's IP address: " . $_SERVER["REMOTE_ADDR"];?>
<?php echo "<br/><br/><br/>";echo "<h2>All information</h2>";foreach ($_SERVER as $key => $value) { echo $key . " = " . $value . "<br/>"; }?>
</body></html>
The $_SERVER is a super global variable, i.e. it's available in all scopes of a PHP script.
$_SERVER info on php.net
PHP functions
• 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.)• PHP has built-in functions but it gives you an option to create your own
functions as well.• There are two parts:• Creating a PHP Function• 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.
Array functionsFunction Description
array() Creates an array
Array chunk() Splits an array into chunks of arrays
Array count values() Returns an array with the number of occurrences for each value
Array flip() Exchanges all keys with their associated values in an array
Array map() Sends each value of an array to a user-made function, which returns new values
Array pop() Deletes the last element of an array
Array push() Inserts one or more elements to the end of an array
Class and object functionsFunction Description
get_class_vars() Get the default properties of the classget_class() Returns the name of the class of an object
get_declared_classes() Returns an array with the name of the defined classes
get_object_vars() Gets the properties of the given objectget_parent_class() Retrieves the parent class name for object or class
method_exists() Checks if the class method existsproperty_exists() Checks if the object or class has a property
Creating a 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:
Sample code<html><head><title>Writing a PHP function</title></head><body><?php/*Defining a functions*/function writeMessage(){echo"Hello";}?></body></html>
Passing parameters• We can pass as many parameters as we want.• They act like variables inside the function.• The following example takes 2 integer parameters and adds them.
• <?php• function addFunction($num1,$num2)• {• $sum=$num1+$num2;• echo "Sum of the 2 numbers is:$sum";• }• addFunction(10,20);• ?>• </body>• </html>
Passing Parameters by reference• It is possible to pass arguments by reference.• A reference to the variable is manipulated rather than modifying its
copy.• An ampersand has to be added to the variable name.• We have to pass parameters by reference when multiple values have
to be returned.
• <?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 $orignum<br />";• ?>• </body>• </html>
• <?php• function addFunction($num1, $num2)• {• $sum = $num1 + $num2;• return $sum;• }• $return_value = addFunction(10, 20);• echo "Returned value from the function : $return_value";• ?>
Form handling• The PHP superglobals $_GET and $_POST are used to collect form-
data. (Superglobals can be accessed by any function.)• When the user fills out the form above and clicks the submit button,
the form data is sent for processing to a PHP filenamed "welcome.php". The form data is sent with the HTTP POST method.
• To display the submitted data you could simply echo all the variables. The "welcome.php" looks like this:• <html>• <body>
Welcome <?php echo $_POST["name"]; ?><br>Your email address is: <?php echo $_POST["email"]; ?>
• </body>• </html>
When to use GET?• Information sent from a form with the GET method is visible to
everyone (all variable names and values are displayed in the URL). GET also has limits on the amount of information to send. The limitation is about 2000 characters. However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.• GET may be used for sending non-sensitive data.• Note: GET should NEVER be used for sending passwords or other
sensitive information!
When to use POST?• Information sent from a form with the POST method is invisible to
others (all names/values are embedded within the body of the HTTP request) and has no limits on the amount of information to send.• Moreover POST supports advanced functionality such as support for
multi-part binary input while uploading files to server.• However, because the variables are not displayed in the URL, it is not
possible to bookmark the page.
Sessions• An alternative way to make data accessible across the various pages of an
entire website is to use php sessions.• 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 the pages on the site during that visit.• The location of the temporary file is determined by setting it in the php.ini file
called session.save_path• Before using session variables we have to set this path.• A session ends after the user loses the browser or after leaving the site, the
server will terminate the session after a predetermined time, usually 30 mins.
What happens when a session is created?• PHP first creates a unique identifier for that particular session which is
a random string of 32hexadecimal string.• A cookie called PHPSESSID is automatically sent to the user’s
computer to store unique identification string.• A file is automatically created on the server in the designated
temporary directory and bears the name of the unique identifier prefixed by sess_ followed by the 32hex string.
Starting a PHP session• A PHP session is started by calling session_start(), it checks if a session
has already started, if not, it starts on. This is usually done at the beginning of the page.• Session variables are stored in an array called $_SESSION, these
variables are accessible during the lifetime of the session.• In the example, a variable counter is registered which increments
each time the page is visited during the session.
<?phpSession_start();If(isset($SESSION[‘counter’])){$_SESSION[‘counter’]+=1;}Else$_SESSION[‘counter’]=1;$msg=“You have visited this page”,$_SESSION[‘counter’];?><?php echo($msg);?>
Destroying a session• A PHP session can be destroyed by session_destroy() function which
does not need any argument and a single call can destroy the session.• Unsetting a single variable :<?phpUnset($_SESSION[‘counter’])?>Call that destroys all the session variables:<?phpSession_destroy()?>
• PHP must be configured correctly in the php.ini file with the details of how your system sends an email.• Open php.ini file available in /etc/ directory and find the section
headed [mail function].• For windows, 2 directives must be supplied.• SMTP : Defines your email server address• sendmail_from which defines your own address
• [mail function]• ;For Win32 only.• SMTP = smtp.secureserver.net• ; For win32 only• Sendmail_from = [email protected]
Emails in PHPThe mail() function allows you to send emails directly from a script.Syntax: (to,subject,message,headers,parameters)To : Required, specifies the receivers of the email (receipient’s email
address)Subject : Required, Cannot contain new line charachters
• Message:Required,Lines should not exceed 70 characters• Headers:Optional, Specifies additional headers like cc, bcc• Parameters: Optional, specifies an additional parameter to the
sendmail program
• As soon as the mail function is called, PHP will attempt to send the email then it will return true if it is successful or false if it fails.• Multiple recipients can be specified as the first argument to the mail()
function in a comma separated list.
<?php$to = [email protected]$subject = “Subject”;$message = “First php email”;$header = “From : [email protected]”;$retval = mail($to,$subject,$message,$hearder)If(retval==true)Echo”Message sent successfully”;ElseEcho”Message could not be sent”;?>
PHP CODING STANDARD Coding standard is required because there may be many developers working on
different modules so if they will start inventing their own standards then source will become very un-manageable and it will become difficult to maintain that source code in future.
Here are several reasons why to use coding specifications:• Your peer programmers have to understand the code you produce. A coding standard
acts as the blueprint for all the team to decipher the code.• Simplicity and clarity achieved by consistent coding saves you from common mistakes.• If you revise your code after some time then it becomes easy to understand that code.• Its industry standard to follow a particular standard to being more quality in software.
There are few guidelines which can be followed while coding in PHP.• Indenting and Line Length - Use an indent of 4 spaces and don't use any tab because different
computers use different setting for tab. It is recommended to keep lines at approximately 75-85 characters long for better code readability.
• Control Structures - These include if, for, while, switch, etc. Control statements should have one space between the control keyword and opening parenthesis, to distinguish them from function calls. You are strongly encouraged to always use curly braces even in situations where they are technically optional.
Examples:if ((condition1) || (condition2)) { action1; } elseif ((condition3) && (condition4)) { action2; } else { default action; }
• Function Calls - Functions should be called with no spaces between the function name, the opening parenthesis, and the first parameter; spaces between commas and each parameter, and no space between the last parameter, the closing parenthesis, and the semicolon. Here's an example:
$var = foo($bar, $baz, $quux); • Function Definitions - Function declarations follow the "BSD/Allman style": function fooFunction($arg1, $arg2 ) { if (condition) { statement; } return $val; }
• Comments - C style comments (/* */) and standard C++ comments (//) are both fine. Use of Perl/shell style comments (#) is discouraged.
• PHP Code Tags - Always use <?php ?> to delimit PHP code, not the <? ?> shorthand. This is required for PHP compliance and is also the most portable way to include PHP code on differing operating systems and setups.
• Variable Names -• Use all lower case letters• Use '_' as the word separator.• Global variables should be prepended with a 'g'.• Global constants should be all caps with '_' separators.• Static variables may be prepended with 's'.
• Make Functions Re-entrant - Functions should not keep static variables that prevent a function from being re-entrant.
• Alignment of Declaration Blocks - Block of declarations should be aligned.
PHP - Predefined Variables
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 File Uploading
• 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• The user opens the page containing a HTML form featuring a text files, a browse button and a
submit button.• The user clicks the browse button and selects a file to upload from the local PC.• The full path to the selected file appears in the text filed then the user clicks the submit
button.• The selected file is sent to the temporary directory on the server.• 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.• 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.
• enctype='multipart/form-data is an encoding type that allows files to be sent through a POST. Quite simply, without this encoding the files cannot be sent through POST. If you want to allow a user to upload a file via a form, you must use this enctype.
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:
$_FILES['file']['tmp_name']- the uploaded file in the temporary directory on the web server.
$_FILES['file']['name'] - the actual name of the uploaded file.
$_FILES['file']['size'] - the size in bytes of the uploaded file.
$_FILES['file']['type'] - the MIME type of the uploaded file.
$_FILES['file']['error'] - the error code associated with this file upload.
• The following example below attempts to copy a file uploaded by the HTML Form listed in previous section page to /var/www/html directory which is document root of your PHP server and it will display all the file's detail upon completion.
• Here is the code of uploader.php script which will take care of uploading a file.• MIME (Multi-Purpose Internet Mail Extensions) is an extension of the original Internet e-mail protocol that lets people use
the protocol to exchange different kinds of data files on the Internet: audio, video, images, application programs, and other kinds
PHP Files & I/O
• Opening a file• Reading 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.
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 file's 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.
PHP for C Developers
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 diferences in PHP and C
• Similarities:• 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 (#).
• 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.
• 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.
• Function names: As you peruse the documentation, you.ll see many function names that seem identical to C functions.
Differences:• 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.• 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.• 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.• 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.
• No structure type: There is no struct 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.
• No pointers: There are no pointers available in PHP, although the typeless 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.
• No prototypes: Functions do not need to be declared before their implementation is defined, as long as the function definition can be found somewhere in the current code file or included files.
• 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 destructors for objects, but there is no free or delete. Destructors are called when the last reference to an object goes away, before the memory is reclaimed.
• Compilation and linking: There is no separate compilation step for PHP scripts.• 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.
Common uses of PHP• PHP performs system functions, i.e. from files on a system it can
create, open, read, write, and close them.• 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.• You add, delete, modify elements within your database thru PHP.• Access cookies variables and set cookies.• Using PHP, you can restrict users to access some pages of your
website.• It can encrypt data.
Advantages:• Open source: It is developed and maintained by a large group of PHP developers, this
will helps in creating a support community, abundant extension library.• Speed: It is relative fast since it uses much system resource.• Easy to use: It uses C like syntax, so for those who are familiar with C, it’s very easy for
them to pick up and it is very easy to create website scripts.• Powerful library support: You can easily find functional modules you need such as PDF,
Graph etc.• Built-in database connection modules: You can connect to database easily using PHP,
since many websites are data/content driven, so we will use database frequently, this will largely reduce the development time of web apps.
• Can be run on many platforms, including Windows, Linux and Mac, it’s easy for users to find hosting service providers.
Disadvantages:• Security : Since it is open sourced, so all people can see the source
code, if there are bugs in the source code, it can be used by people to explore the weakness of PHP• Not suitable for large applications: Hard to maintain since it is not
very modular.