PHP Magic Variables and Magic functions in a detailed

Magic variable

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

However, many constants are defined by different extensions, and are only present when the extensions are loaded, either dynamically after loading, or they are included at compile time.

There are eight magic constants whose values change as they change position in the code.

For example, the value of __line__ depends on the row it is in the script to determine. These special constants are case-insensitive, as follows:

__line__

The current line number in the file.

Instance:

<? PHP Echo ' This is the first '  __line__ . ' "Line";? >

The result of the above example output is:

This is the "2" line.

__file__

The full path and file name of the file. If used in the included file, returns the file name that is included.

From PHP 4.0.2, __file__ always contains an absolute path (if it is a symbolic connection, the resolved absolute path), and the previous version sometimes contains a relative path.

Instance:

<? PHP Echo ' The file is located in ' '  __file__ . ' "';? >

The result of the above example output is:

The file is located in the "E:\wamp\www\test\index.php"

__dir__

The directory where the file resides. If used in the included file, returns the directory where the included files are located.

It is equivalent to DirName (__file__). Unless it is a root directory, the name in the directory does not include the trailing slash. (New in PHP 5.3.0)

Instance:

<? PHP Echo ' The file is located '  . __dir__. "';? ' >

The result of the above example output is:

The file is located in the "E:\wamp\www\test"

__function__

The name of the function (PHP 4.3.0 new addition). From PHP 5 This constant returns the name (case-sensitive) when the function is defined. In PHP 4, this value is always in lowercase letters.

Instance:

<? PHP function  echo  __function__  ;} Test ();? >

The result of the above example output is:

The function name is: Test

__class__

The name of the class (PHP 4.3.0 new addition). From PHP 5 This constant returns the name of the class when it is defined (case-sensitive).

In PHP 4, this value is always in lowercase letters. The class name includes its declared action area (for example, Foo\bar). Note since PHP 5.4, __CLASS__ has also worked for trait. When used in the trait method, __class__ is the name of the class that invokes the trait method.

Instance:

<? PHP class  function  _print () {  echo ' class is named: '  __class__ . "<br>";   Echo  __function__  ; }} $t New test (); $t-_print ();? >

The result of the above example output is:

The class name is: Test
The function name is: _print

__trait__

Trait's name (PHP 5.4.0 new Plus). Since PHP 5.4.0, PHP has implemented a method of code reuse, called traits.

The Trait name includes its declared function area (for example, Foo\bar).

Members inherited from the base class are overwritten by the Myhelloworld method in the inserted Sayworld Trait. Its behavior is consistent with the methods defined in the Myhelloworld class. The precedence is that methods in the current class override the Trait method, and the trait method overrides the method in the base class.

<?PHPclassBase { Public functionSayHello () {Echo' Hello '; }} {     Public functionSayHello () {Parent::SayHello (); Echo' world! '; }}classMyhelloworldextendsBase {}$o=NewMyhelloworld ();$o-SayHello ();?>

The above routines will output:

Hello world!

__method__

The method name of the class (PHP 5.0.0 new addition). Returns the name of the method when it is defined (case-sensitive).

Instance:

<? PHP function  echo  __method__  ;} Test ();? >

The result of the above example output is:

The function name is: Test

__namespace__

The name of the current namespace (case-sensitive). This constant is defined at compile time (PHP 5.3.0 is new).

Instance:

<? phpnamespace MyProject; Echo // output "MyProject"?>

The result of the above example output is:

The namespace is: "MyProject"

Magic function

__construct ()
Called when an object is instantiated,
When __construct and a function with a class name are present, __construct is called and the other is not called.

__destruct ()
Called when an object is deleted or when an object operation terminates.

__call ()
Object calls a method,
If the method exists, it is called directly;
If it does not exist, it will call the __call function.

__get ()
When reading the properties of an object,
If the attribute exists, the property value is returned directly;
If it does not exist, the __get function is called.

__set ()
When you set the properties of an object,
If the attribute exists, the value is directly assigned;
If it does not exist, the __set function is called.

__tostring ()
Called when an object is printed. such as Echo $obj; or print $obj;

__clone ()
Called when the object is cloned. such as: $t =new Test (); $t 1=clone $t;

__sleep ()
Serialize before being called. If the object is relatively large, want to cut a bit of the east and then serialize, you can consider this function.

__wakeup ()
Unserialize is called to do some initialization of the object.

__isset ()
Called when detecting whether an object's properties exist. such as: Isset ($c->name).

__unset ()
Called when a property of an object is unset. such as: unset ($c->name).

__set_state ()
Called when the Var_export is called. Use the return value of __set_state as the return value of Var_export.

__autoload ()
When an object is instantiated, the method is called if the corresponding class does not exist.

The above is the whole content of this article, whether the small partners to magic variables and magic function has a new understanding of it, I hope you like the content of this article.

PHP Magic Variables and Magic functions in a detailed