ATEXIT(3)                                           Linux Programmer's Manual                                          ATEXIT(3)



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

SYNOPSIS
       #include <stdlib.h>

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

DESCRIPTION
       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.1-2001  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.

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

CONFORMING TO
       SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

NOTES
       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 functions 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.1-2001  says  that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered
       using atexit(3)) is undefined.  On some systems (but not Linux), this can result in an infinite recursion; portable  pro-
       grams should not invoke exit(3) inside a function registered using atexit(3).

       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.

       POSIX.1-2001 says that the result is undefined if longjmp(3) is used to terminate execution of one of the functions  reg-
       istered atexit().

   Linux Notes
       Since  glibc  2.2.3, atexit() (and on_exit(3)) can be used within a shared library to establish functions that are called
       when the shared library is unloaded.

EXAMPLE
       #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);
       }

SEE ALSO
       _exit(2), exit(3), on_exit(3)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-12-05                                                  ATEXIT(3)