Magic variables
PHP provides a large number of predefined constants to any script it runs.
However, many constants are defined by different extension libraries and 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 not case-sensitive, as follows:
__LINE__
The current line number in the file.
Example:
The code is as follows:
echo 'This is line " ' . __LINE__ . ' ";
?>
The output result of the above example is:
The code is as follows:
This is line “2”
__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), while versions before that sometimes contained a relative path.
Example:
The code is as follows:
echo 'The file is located at " ' . __FILE__ . ' " ';
?>
The output result of the above example is:
The code is as follows:
The file is located at " E:wampwwwtestindex.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:
The code is as follows:
echo 'The file is located at " ' . __DIR__ . ' " ';
?>
The output result of the above example is:
The code is as follows:
The file is located at " E:wampwwwtest "
__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:
The code is as follows:
function test() {
echo 'The function name is:' . __FUNCTION__ ;
}
test();
?>
The output result of the above example is:
The code is as follows:
Function name: test
__CLASS__
The name of the class (new 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 lowercase. 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:
The code is as follows:
class test {
function _print() {
echo 'Class name:' . __CLASS__ . "
";
echo 'The function name is:' . __FUNCTION__ ;
}
}
$t = new test();
$t->_print();
?>
The output result of the above example is:
Class name: test
Function name: _print
__TRAIT__
Trait name (new 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.
The code is as follows:
class Base {
public function sayHello() {
echo 'Hello ';
}
}
{
public function sayHello() {
parent::sayHello();
echo 'World!';
}
}
class MyHelloWorld extends Base {
}
$o = new MyHelloWorld();
$o->sayHello();
?>
The above routine will output:
The code is as follows:
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:
Copy the code The code is as follows:
function test() {
echo 'Function name:' . __METHOD__ ;
}
test();
?>
The output result of the above example is:
The code is as follows:
Function name: test
__NAMESPACE__
The name of the current namespace (case sensitive). This constant is defined at compile time (new in PHP 5.3.0).
Example:
The code is as follows:
namespace MyProject;
echo 'The namespace is: "', __NAMESPACE__, '"'; // Output "MyProject"
?>
The output result of the above example is:
The code is as follows:
The namespace is: "MyProject"
Magic function
__construct()
Called when an object is instantiated,
When __construct and a function with the class name exist at the same time, __construct will be called and the other will not be called.
__destruct()
Called when an object is deleted or when the object operation terminates.
__call()
The object calls a method,
If the method exists, call it directly;
If it does not exist, the __call function will be called.
__get()
When reading the properties of an object,
If the attribute exists, the attribute value is returned directly;
If it does not exist, the __get function will be called.
__set()
When setting the properties of an object,
If the attribute exists, assign the value 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()
Called when cloning an object. For example: $t=new Test();$t1=clone $t;
__sleep()
serialize was called before. If the object is relatively large and you want to delete a little bit before serializing it, you can consider this function.
__wakeup()
It is called when unserialize is used to do some object initialization work.
__isset()
Called when checking whether an object's property exists. For example: isset($c->name).
__unset()
Called when unsetting a property of an object. For example: unset($c->name).
__set_state()
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, this method is called if the corresponding class does not exist.
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