### 2.6 `atexit`—request execution of functions at program exit

Synopsis

         #include <stdlib.h>
         int atexit (void (*function)(void));

Description
You can use `atexit` to enroll functions in a list of functions that will be called when your program terminates normally. The argument is a pointer to a user-defined function (which must not require arguments and must not return a result).

The functions are kept in a LIFO stack; that is, the last function enrolled by `atexit` will be the first to execute when your program exits.

There is no built-in limit to the number of functions you can enroll in this list; however, after every group of 32 functions is enrolled, `atexit` will call `malloc` to get space for the next part of the list. The initial list of 32 functions is statically allocated, so you can always count on at least that many slots available.

Returns
`atexit` returns `0` if it succeeds in enrolling your function, `-1` if it fails (possible only if no space was available for `malloc` to extend the list of functions).

Portability
`atexit` is required by the ANSI standard, which also specifies that implementations must support enrolling at least 32 functions.

Supporting OS subroutines required: `close`, `fstat`, `isatty`, `lseek`, `read`, `sbrk`, `write`.