Detailed explanation of PHP magic variables and magic functions

Magic Variables

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

However, many constants are defined by different extension libraries. They will only appear when these extension libraries are loaded, or after dynamic loading, or have been included during compilation.

There are eight magic constants whose values ​​change depending on their position in the code.

For example, the value of __LINE__ depends on the line it is located in the script. These special constants are case-insensitive and are as follows:

__LINE__

The current line number in the file.

Example:

<?php
echo &#39;这是第 “ &#39;  . __LINE__ . &#39; ” 行&#39;;
?>

The output result of the above example is:

这是第 “ 2 ” 行

__FILE__

The full path and file name of the file. If used within an included file, returns the name of the included file.

Since PHP 4.0.2, __FILE__ always contains an absolute path (or the resolved absolute path in the case of a symbolic link), whereas previous versions sometimes contained a relative path.

Example:

?php
echo '该文件位于 “ '  . __FILE__ . ' ” ';
?>

The output result of the above example is:

该文件位于 “ E:\wamp\www\test\index.php ”

__DIR__

The directory where the file is located. If used within an included file, returns the directory where the included file is located.

It is equivalent to dirname(__FILE__). Directory names do not include the trailing slash unless they are the root directory. (New in PHP 5.3.0)

Example:

<?php
echo &#39;该文件位于 “ &#39;  . __DIR__ . &#39; ” &#39;;
?>

The output result of the above example is:

该文件位于 “ E:\wamp\www\test ”

__FUNCTION__

Function name (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the function as it was defined (case sensitive). In PHP 4 this value is always lowercase.

Example:

?php
function test() {
 echo  '函数名为：' . __FUNCTION__ ;
}
test();
?>

The output result of the above example is:

函数名为：test

__CLASS__

The name of the class (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the class when it was defined (case sensitive).

In PHP 4 this value is always lower case. The class name includes the scope in which it is declared (e.g. FooBar). Note that since PHP 5.4 __CLASS__ also works for traits. When used within a trait method, __CLASS__ is the name of the class that calls the trait method.

Example:

<?php
class test {
 function _print() {
  echo &#39;类名为：&#39;  . __CLASS__ . "<br>";
  echo  &#39;函数名为：&#39; . __FUNCTION__ ;
 }
}
$t = new test();
$t->_print();
?>

The output result of the above example is:

Class name: test
Function name: _print

__TRAIT__

Trait name (newly added in PHP 5.4.0). Since PHP 5.4.0, PHP implements a method of code reuse called traits.

The Trait name includes the scope in which it is declared (e.g. FooBar).

Members inherited from the base class are overridden by the MyHelloWorld method in the inserted SayWorld Trait. Its behavior is consistent with the methods defined in the MyHelloWorld class. The order of precedence is that methods in the current class override trait methods, which in turn override methods in the base class.

<?php
class Base {
    public function sayHello() {
        echo &#39;Hello &#39;;
    }
}
 {
    public function sayHello() {
        parent::sayHello();
        echo &#39;World!&#39;;
    }
}
class MyHelloWorld extends Base {
    
}
$o = new MyHelloWorld();
$o->sayHello();
?>

The above routine will output:

Hello World!

METHOD__

The method name of the class (newly added in PHP 5.0.0). Returns the name of the method as it was defined (case-sensitive).

Example:

<?php
function test() {
 echo  &#39;函数名为：&#39; . __METHOD__ ;
}
test();
?>

The output result of the above example is:

函数名为：test

__NAMESPACE__

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

Example:

<?php
namespace MyProject;
echo &#39;命名空间为："&#39;, __NAMESPACE__, &#39;"&#39;; // 输出 "MyProject"
?>

The output result of the above example is:

命名空间为："MyProject"

Magic function

__construct()
is called when instantiating an object,
When __construct and a function with the class name and function name exist at the same time, __construct will is called, the other is not called.

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

__call()
The object calls a method.
If the method exists, it will be called directly;
If it does not exist, the __call function will be called.

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

__set()
When setting the attributes of an object,
If the attribute exists, the value will be assigned directly;
If it does not exist, the __set function will be called.

__toString()
Called when printing an object. Such as echo $obj; or print $obj;

__clone()
is called when cloning an object. For example: $t=new Test();$t1=clone $t;

__sleep()
serialize was called before. If the object is relatively large and you want to delete a few things before serializing, you can consider this function.

__wakeup()
It is called when unserialize and does some object initialization work.

__isset()
Called when checking whether an object’s attributes exist. For example: isset($c->name).

__unset()
Called when unsetting the properties of an object. For example: unset($c->name).

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

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

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