Understanding and application of relevant knowledge about PHP magic variables

PHP Magic variables play an important role in PHP. This article explains them in detail.

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 and are as follows:

__LINE__

The current line number in the file.

Example

The output result of the above example is:

This is the full path and file name of the file in line "2"

__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:

Example

The above example output The result is:

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

##__DIR__

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

Above example The output result is:

The file is located in "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

<?phpfunction test() {
    echo  &#39;函数名为：&#39; . __FUNCTION__ ;}test();?>

The output result of the above example is:

The function name is: 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. Foo\Bar). 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

<?phpclass 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 (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 (for example, Foo\Bar).

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.

Example

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

The above routine will output:

Hello World!

__METHOD__

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

Example

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

The output result of the above example is:

The function name is: test

__NAMESPACE__

Current namespace name (case sensitive). This constant is defined at compile time (new in PHP 5.3.0).

Example:

Example

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

The output result of the above example is:

The namespace is: "MyProject"

This article provides a detailed understanding of PHP's magic variables. For more learning materials, please pay attention to the PHP Chinese website.

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