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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 success-
       ful 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 non-zero 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 programs 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 func-
       tions registered 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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-12-05                         ATEXIT(3)