(PECL weakref >= 0.1.0) Checks whether the object referenced still exists

(PHP 4, PHP 5, PHP 7) Gets the value of an environment variable

(PHP 5, PHP 7) Prints a backtrace void debug_print_backtrace

(PHP 5 >= 5.5.5, PHP 7, PECL ZendOpcache > 7.0.2) Get status information about the cache

(PHP 5 >= 5.3.0, PHP 7) Activates the circular reference collector

(PECL apc >= 3.1.1) Get current item public

(PHP 4 >= 4.3.0, PHP 5, PHP 7) Gets the current include_path configuration option

(PECL apcu >= 4.0.0) Cache a variable in the data store

(PECL weakref >= 0.2.0) Returns the value pointed to by a certain object

(PECL apd 0.2-0.4) Throw an error, a callstack and then exit