Manpages - atexit.3

atexit - register a function to be called at normal process termination

  #include <stdlib.h>

  int atexit(void (*function)(void));

The *atexit*() function registers the given function to be called at normal process termination, either via *exit*(3) or via return from the program’s /main/(). Functions so registered are called in the reverse order of their registration; no arguments are passed.

The same function may be registered multiple times: it is called once for each registration.

POSIX.1 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered. The actual limit supported by an implementation can be obtained using *sysconf*(3).

When a child process is created via *fork*(2), it inherits copies of its parent’s registrations. Upon a successful call to one of the *exec*(3) functions, all registrations are removed.

The *atexit*() function returns the value 0 if successful; otherwise it returns a nonzero value.

For an explanation of the terms used in this section, see *attributes*(7).

POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

Functions registered using *atexit*() (and *on_exit*(3)) are not called if a process terminates abnormally because of the delivery of a signal.

If one of the registered functions calls *_exit*(2), then any remaining functions are not invoked, and the other process termination steps performed by *exit*(3) are not performed.

POSIX.1 says that the result of calling *exit*(3) more than once (i.e., calling *exit*(3) within a function registered using *atexit*()) is undefined. On some systems (but not Linux), this can result in an infinite recursion; portable programs should not invoke *exit*(3) inside a function registered using *atexit*().

The *atexit*() and *on_exit*(3) functions register functions on the same list: at normal process termination, the registered functions are invoked in reverse order of their registration by these two functions.

According to POSIX.1, the result is undefined if *longjmp*(3) is used to terminate execution of one of the functions registered using *atexit*().

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>

  void
  bye(void)
  {
      printf("That was all, folks\n");
  }

  int
  main(void)
  {
      long a;
      int i;

      a = sysconf(_SC_ATEXIT_MAX);
      printf("ATEXIT_MAX = %ld\n", a);

      i = atexit(bye);
      if (i != 0) {
          fprintf(stderr, "cannot set exit function\n");
          exit(EXIT_FAILURE);
      }

      exit(EXIT_SUCCESS);
  }

*_exit*(2), *dlopen*(3), *exit*(3), *on_exit*(3)

This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.