Detailed explanation of magic constant examples in php

What are magic constants?

When explaining PHP constants, we know that most of the constants in PHP are unchanged, but there are 8 predefined constants that will change as the location of the code where they are located changes. These 8 A constant is called a magic constant. These special constants are not case-sensitive.

PHP's "magic constants" are as follows:

##FunctionDetection type__LINE__The current line number in the file. __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. __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) __FUNCTION__ Function name (New 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. __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 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 in a trait method, __CLASS__ is the name of the class that calls the trait method __TRAIT__The name of the Trait (new in PHP 5.4.0). Since PHP 5.4 this constant returns the name of the trait as it was defined (case-sensitive). The Trait name includes the scope in which it is declared (for example, Foo\Bar)__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). __NAMESPACE__The name of the current namespace (case-sensitive). This constant is defined at compile time (new in PHP 5.3.0).

The "__" in the above table is two underscores, not one "_".

Magic constants are often used to obtain current environment information or record logs.

Let me take a look at the usage of these magic constants:

__LINE__ Get the current line number in the file.

Example

<?PHP
header("content-type:text/html;charset=utf-8");
echo "这是第 ". __LINE__ ."行";
echo "<br/>";
?>

Code running result:

__FILE__ Get the full path and file name of the file, if When used in an included file, returns the included file name.

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

Example

<?php
header("content-type:text/html;charset=utf-8");
echo "该文件位于 ". __DIR__ ."文件夹下";
echo "<br/>";
?>

Code running result:

__FUNCTION__ Get the name of the function when it is defined (differentiate uppercase and lowercase), only the function name

instance

<?php
header("content-type:text/html;charset=utf-8");
function Test() {
    echo  "该函数名为：". __FUNCTION__ ;
    echo "<br/>";
}
Test();
?>

code running result is returned:

__CLASS__ Get the The name when the class is defined (case-sensitive)

Example

<?php
header("content-type:text/html;charset=utf-8");
class test {
    function show() {
        echo "该类名为：". __CLASS__ . "<br>";
        echo "该函数名为：". __FUNCTION__ ;
        echo "<br/>";
    }
}
$t = new test();
$t->show();
?>

Code running result:

__METHOD__ Get the name of the method when it is defined (case-sensitive). If the function is in a class, return the class method name,

That is: Class name::Method name.

Example

<?php
    header("content-type:text/html;charset=utf-8");
    function test1() {
        echo  "该函数名为：". __METHOD__ ;
        echo "<br/>";
    }
    test1();
    ?>
    <?php
    class chhua{
        function test(){
            //返回类方法的名称
            echo __METHOD__;
        }
    }
    $e=new chhua();
    $e->test();//输出：chhua::test
    ?>

Code running result:

##__NAMESPACE__ The name of the current namespace (case-sensitive)

<?php
namespace MyProject;

echo &#39;"&#39;, __NAMESPACE__, &#39;"&#39;; // 输出 "MyProject"
?>

Code running result:

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