PHP fallback global functions/constants

In a namespace, when PHP encounters an unqualified class, function, or constant name, it uses a different precedence policy to resolve the name. The class name always resolves to the name in the current namespace. Therefore, you must use a fully qualified name when accessing a class name that is inside the system or that is not contained in a namespace, for example:

Example #1 Accessing the global class in the namespace

<?php    namespace a\b\c;    Class Exception extends \exception {}    $a = new Exception (' Hi ');//$a is an object of class a\b\c\exception    $b = new \exception (' Hi '); $b is an object of class Exception    $c = new Arrayobject;//Fatal error, A\b\c\arrayobject class not found?>

For functions and constants, if the function or constant does not exist in the current namespace, PHP will fallback to use the function or constant in the global space.

Example a fallback global function/constant in #2 namespace

<?php    namespace a\b\c;    Const E_ERROR =;    function strlen ($str)    {        return \strlen ($STR)-1;    }    echo E_error, "\ n"; Output "Ini_all"    echo, "\ n",//Output "7"-use global constants Ini_all    echo strlen (' Hi '), "\ n",//Output "1"    if (Is_array (' Hi ')) {//output "is not an array"        echo "is array\n";    } else {        echo "was not array\n";    }? >

