php global space

If no namespace is defined, all classes and functions are defined in the global space, just like before PHP introduced the namespace concept. Prefixing the name with means that the name is in the global space, even if the name is in another namespace.

Use global space instructions

<?php
    namespace A\B\C;
    /* 这个函数是 A\B\C\fopen */
    function fopen() {
        /* ... */
        $f = \fopen(...); // 调用全局的fopen函数
        return $f;
    }
?>