PHP(HYPER TEXT PREPROCESSOR)

PHP is a scripting language originally designed for producing dynamic web pages. It has evolved to include a command line interface capability and can be used in standalone graphical applications.[2] While PHP was originally created by Rasmus Lerdorf in 1995, the main implementation of PHP is now produced by The PHP Group and serves as the de facto standard for PHP as there is no formal specification.[3] PHP is free software released under the PHP License, which is incompatible with the GNU General Public License (GPL) due to restrictions on the use of the term PHP.[4] PHP is a widely-used general-purpose scripting language that is especially suited for web development and can be embedded into HTML. It generally runs on a web server, which is configured to take PHP code as input and create web page content as output. It can be deployed on most web servers and on almost every operating system and platform free of charge.PHP is installed on over 20 million websites and 1 million web servers

PHP syntax and semantics

Syntax-highlighted PHP code embedded within HTML

PHP only parses code within its delimiters. Anything outside its delimiters is sent directly to the output and is not parsed by PHP. The most common delimiters are , which are open and close delimiters respectively. and delimiters are also available. Short tags can be used to start PHP code, . These tags are commonly used, but like ASP-style tags (<% or <%= and %>), they are less portable as they can be disabled in the PHP configuration. For this reason, the use of short tags and ASP-style tags is discouraged.[53] The purpose of these delimiters is to separate PHP code from non-PHP code, including HTML.[54]

The first form of delimiters, , in XHTML and other XML documents, creates correctly formed XML 'processing instructions'.[55] This means that the resulting mixture of PHP and other markup is well-formed XML.

Variables are prefixed with a dollar symbol and a type does not need to be specified in advance. Unlike function and class names, variable names are case sensitive. Both double-quoted ("") and heredoc strings allow the ability to embed a variable's value into the string.[56] PHP treats newlines as whitespace in the manner of a free-form language (except when inside string quotes), and statements are terminated by a semicolon.[57] PHP has three types of comment syntax: /* */ marks block and inline comments; // as well as # are used for one-line comments.[58] The echo statement is one of several facilities PHP provides to output text (e.g. to a web browser).

In terms of keywords and language syntax, PHP is similar to most high level languages that follow the C style syntax. If conditions, for and while loops, and function returns are similar in syntax to languages such as C, C++, Java and Perl.

PHP

Data Type

PHP stores whole numbers in a platform-dependent range. This range is typically that of 32-bit signed integers. Unsigned integers are converted to signed values in certain situations; this behavior is different from other programming languages.[59] Integer variables can be assigned using decimal (positive and negative), octal, and hexadecimal notations. Floating point numbers are also stored in a platform-specific range. They can be specified using floating point notation, or two forms of scientific notation.[60] PHP has a native Boolean type that is similar to the native Boolean types in Java and C++. Using the Boolean type conversion rules, non-zero values are interpreted as true and zero as false, as in Perl and C++.[60] The null data type represents a variable that has no value. The only value in the null data type is NULL.[60] Variables of the "resource" type represent references to resources from external sources. These are typically created by functions from a particular extension, and can only be processed by functions from the same extension; examples include file, image, and database resources.[60] Arrays can contain elements of any type that PHP can handle, including resources, objects, and even other arrays. Order is preserved in lists of values and in hashes with both keys and values, and the two can be intermingled. PHP also supports strings, which can be used with single quotes, double quotes, or heredoc syntax.
The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.[62]

Functions

PHP has hundreds of base functions and thousands more via extensions. These functions are well documented on the PHP site, however, the built-in library has a wide variety of naming conventions and inconsistencies. PHP currently has no functions for thread programming.

Functions are not first-class functions and can only be referenced by their name, directly or dynamically by a variable containing the name of the function. [64] User-defined functions can be created at any time without being prototyped.[64] Functions can be defined inside code blocks, permitting a run-time decision as to whether or not a function should be defined. Function calls must use parentheses, with the exception of zero argument class constructor functions called with the PHP new operator, where parentheses are optional. PHP supports quasi-anonymous functions through the create_function() function, although they are not true anonymous functions because anonymous functions are nameless, but functions can only be referenced by name, or indirectly through a variable $function_name();, in PHP.[64]

5.3 and newer

PHP gained support for closures. True anonymous functions are supported using the following syntax:
function getAdder($x) {
return function ($y) use ($x) {
return $x + $y;
};
}
$adder = getAdder(8);
echo $adder(2); // prints "10"
Here, getAdder() function creates a closure using parameter $x (keyword "use" forces getting variable from context), which takes additional argument $y and returns it to the caller. Such a function can be stored, given as the parameter to another functions, etc. For more details see Lambda functions and closures RFC.

Objects

Basic object-oriented programming functionality was added in PHP 3 and improved in PHP 4.[3] Object handling was completely rewritten for PHP 5, expanding the feature set and enhancing performance.[65] In previous versions of PHP, objects were handled like primitive types.[65] The drawback of this method was that the whole object was copied when a variable was assigned or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value. PHP 5 introduced private and protected member variables and methods, along with abstract classes and final classes as well as abstract methods and final methods. It also introduced a standard way of declaring constructors and destructors, similar to that of other object-oriented languages such as C++, and a standard exception handling model. Furthermore, PHP 5 added interfaces and allowed for multiple interfaces to be implemented. There are special interfaces that allow objects to interact with the runtime system. Objects implementing ArrayAccess can be used with array syntax and objects implementing Iterator or IteratorAggregate can be used with the foreach language construct. There is no virtual table feature in the engine, so static variables are bound with a name instead of a reference at compile time.

If the developer creates a copy of an object using the reserved word clone, the Zend engine will check if a __clone() method has been defined or not. If not, it will call a default __clone() which will copy the object's properties. If a __clone() method is defined, then it will be responsible for setting the necessary properties in the created object. For convenience, the engine will supply a function that imports the properties of the source object, so that the programmer can start with a by-value replica of the source object and only override properties that need to be changed.