PHP Interview Questions - Magic Contant,Methods and Quotes

What is Magic Constant?

PHP provides a large number of predefined constants to any script which it runs.There are seven 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 with symlinks resolved whereas in older versions it contained relative path under some circumstances.
__DIR__	The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)
__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).
__NAMESPACE__	The name of the current namespace (case-sensitive). This constant is defined in compile-time (Added in PHP 5.3.0).

What is Magic Methods?

The function names __construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __toString(), __invoke(), __set_state() and __clone() are magical in PHP classes. You cannot have functions with these names in any of your classes unless you want the magic functionality associated with them.

What is Magic Quotes?

Â This feature has been DEPRECATED as of PHP 5.3.0. Relying on this feature is highly discouraged.When ON, all ' (single-quote), " (double quote), \ (backslash) and NULL characters are escaped with a backslash automatically. This is identical to what addslashes()does.

There are three magic quote directives:

magic_quotes_gpc Affects HTTP Request data (GET, POST, and COOKIE). Cannot be set at runtime, and defaults to on in PHP. See also get_magic_quotes_gpc().

magic_quotes_runtime If enabled, most functions that return data from an external source, including databases and text files, will have quotes escaped with a backslash. Can be set at runtime, and defaults to off in PHP. See also set_magic_quotes_runtime() and get_magic_quotes_runtime().

magic_quotes_sybase If enabled, a single-quote is escaped with a single-quote instead of a backslash. If on, it completely overrides magic_quotes_gpc. Having both directives enabled means only single quotes are escaped as ''. Double quotes, backslashes and NULL's will remain untouched and unescaped. See also ini_get() for retrieving its value.

What is register global?

This feature has beenÂ DEPRECATEDÂ as of PHP 5.3.0. Relying on this feature is highly discouraged.

A common security problem with PHP is theÂ register_globalsÂ setting in PHP's configuration file (php.ini). This setting (which can be eitherÂ OnÂ orÂ Off) tells whether or not to register the contents of the EGPCS (Environment, GET, POST, Cookie, Server) variables as global variables. For example, ifÂ register_globalsÂ is on, the urlÂ http://www.example.com/test.php?id=3will declareÂ $idÂ as aÂ global variableÂ with no code required. Similarly,Â $DOCUMENT_ROOTÂ would also be defined, since it is part of theÂ $_SERVERÂ 'superglobal' array. These two examples are the equivalent of placing the following code at the beginning of a script:

$id = $_GET['id'];

$DOCUMENT_ROOT = $_SERVER['DOCUMENT_ROOT'];

This feature is a great security risk, and you should ensure that register_globals is Off for all scripts (as of PHP 4.2.0 this is the default). It's preferred to go through PHP Predefined Variables instead, such as the superglobal $_REQUEST. Even more secure is to further specify by using: $_ENV, $_GET, $_POST, $_COOKIE, or $_SERVER instead of using the more general superglobal $_REQUEST.

How can we parse URL?

mixed = parse_url ( string $url [, int $component = -1 ] )

$url = The URL to parse. Invalid characters are replaced by _.

$component = Specify one of PHP_URL_SCHEME, PHP_URL_HOST, PHP_URL_PORT, PHP_URL_USER, PHP_URL_PASS, PHP_URL_PATH, PHP_URL_QUERY or PHP_URL_FRAGMENT to retrieve just a specific URL component as a string .

<?php$urlÂ =Â 'http://username:password@hostname/path?arg=value#anchor';print_r(parse_url($url));echoÂ parse_url($url,Â PHP_URL_PATH);?>

Array(
[scheme] => http
[host] => hostname
[user] => username
[pass] => password
[path] => /path
[query] => arg=value
[fragment] => anchor
)

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