Overview

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.

1. There are eight magic constants whose values ??change as their positions in the code change

For example, the value of __LINE__ It depends on which line it is in the script. These special constants are not case-sensitive

See the following table for details:

You can’t learn by just looking at it. Let’s see the output results from examples. Bar
Example: The code is as follows

<?php
//__LINE__  文件中當(dāng)前行號__________________________
echo '這是第 “ '  . __LINE__ . ' ” 行';
echo "<hr/>";
//__FILE__  文件的完整路徑和文件名__________________
echo '該文件位于 “ '  . __FILE__ . ' ” ';
echo "<hr/>";
//__DIR__  文件所在的目錄___________________________
echo '該文件位于 “ '  . __DIR__ . ' ” ';
echo "<hr/>";
//__LINE__  文件中當(dāng)前行號__________________________
echo '這是第 “ '  . __LINE__ . ' ” 行';
echo "<hr/>";
//__FUNCTION__  函數(shù)名稱____________________________
function test() {
    echo  '函數(shù)名為：' . __FUNCTION__ ;
}
test();
echo "<hr/>";
//__CLASS__  類的名稱_______________________________
class c {
    function _print() {
        echo '類名為：'  . __CLASS__ . "<br>";
        echo  '函數(shù)名為：' . __FUNCTION__ ;
    }
}
$t = new c();
$t->_print();
echo "<hr/>";
?>

Note: Please understand the following magic constants first, and there will be details in subsequent chapters

Note: Pay attention to the php version problem. Inappropriate versions will report errors