学习-PHP-继承类-全局变量

今天写PHP脚本，发现在继承类的子类中竟然无法使用全局变量；

问题：config.php

                            $C = 1;

           a.php 

                             class A;

          b.php 

                        require config.php

                       class B extends A;

                        global $C;//在此不管用

解决方法：config.php

                            $C = 1;

           a.php 

                           require config.php 

                           class A;

          b.php                        

                        class B extends A;

                        global $C;//在此管用