Detailed explanation of magic constants in PHP

Constant is an identifier (name) of a simple value. Once constant is defined, it is not allowed to be changed, but everything has Exception, PHP has built-in Magic Constants, which will produce different values ​​as the position changes. This article will take you to learn about the Magic Constants in PHP.

1.__LINE__

<?php

echo __LINE__."<br>";//3

echo __LINE__."<br>";//5

?>

The current line number in the file.​

2.__FILE__

<?php
        echo __FILE__."<br>";//F:\learnlog\zend\php\magic.php
?>

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

##3.__DIR__##

<?php
        echo __DIR__."<br>";//F:\learnlog\zend\php
?>

4.__METHOD__

<?php
function sum(){
    echo __METHOD__."<br>";
}
sum();//输出：sum
?>

5.__CLASS__

<?php
class People{
  
  static function sum(){
     echo __CLASS__;
  }
}
People::sum();//People
?>

6.__NAMESPACE__

<?php
namespace Controller;
class People{
  
  static function sum(){
     echo __NAMESPACE__;
  }
}
People::sum();//Controller
?>

7. __TRAIT__

<?php
trait A{
     function traitName() 
     {echo __TRAIT__;}
 }
 trait B {
     use A;
 }
 class Test {
     use B;
 }
 (new Test)->traitName(); //A
?>

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