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 termina-
       tion, 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 registra-
       tion.

       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  registra-
       tions.   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 termi-
       nates 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 per-
       formed.

       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())  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 regis-
       tration by these two functions.

       POSIX.1-2001  says  that the result is undefined if longjmp(3) is used to terminate execu-
       tion of one of the functions registered atexit().

   Linux notes
       Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a shared library to estab-
       lish 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 3.53 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)