这里显示系统所支持的所有函数,和自定义函数
Array
(
    [internal] => Array
        (
            [0] => zend_version
            [1] => func_num_args
            [2] => func_get_arg
            [3] => func_get_args
            [4] => strlen
            [5] => strcmp
            [6] => strncmp
            [7] => strcasecmp
            [8] => strncasecmp
            [9] => each
            [10] => error_reporting
            [11] => define
            [12] => defined
            [13] => get_class
            [14] => get_called_class
            [15] => get_parent_class
            [16] => method_exists
            [17] => property_exists
            [18] => class_exists
            [19] => interface_exists
            [20] => trait_exists
            [21] => function_exists
            [22] => class_alias
            [23] => get_included_files
            [24] => get_required_files
            [25] => is_subclass_of
            [26] => is_a
            [27] => get_class_vars
            [28] => get_object_vars
            [29] => get_class_methods
            [30] => trigger_error
            [31] => user_error
            [32] => set_error_handler
            [33] => restore_error_handler
            [34] => set_exception_handler
            [35] => resto