How to Access Global Classes and Namespaces in PHP

M66 2025-06-17

Introduction

In PHP, when the parser encounters an unqualified identifier (such as a class or function name), it defaults to parsing it as the current namespace. Therefore, to access PHP's predefined classes, you must reference them by their fully qualified name using the \

Included files will default to the global namespace. Therefore, to reference a class from an included file, you must add the \ prefix to the class name.

Example

# test1.php
<?php
class myclass {
    function hello() {
        echo "Hello World";
    }
}
?>

When this file is included in another PHP script, the class must be referenced with the \ prefix.

Example

# test2.php
<?php
include 'test1.php';

class testclass extends \myclass {
    function hello() {
        echo "Hello PHP";
    }
}

$obj1 = new \myclass();
$obj1->hello();

$obj2 = new testclass();
$obj2->hello();
?>

Output

When running the above code, you will see the following output:

Hello World
Hello PHP

Through the above examples, you can clearly understand how to access global classes in PHP and how to reference them across different namespaces.