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atexit(3)

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 nor‐
       mal process termination, either via exit(3) or via return from the pro‐
       gram'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.

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

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

       allbox;  lb  lb  lb  l  l  l.   Interface Attribute Value  T{  atexit()
       T}   Thread safety    MT-Safe


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

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 registered functions calls _exit(2), then any remaining
       functions are not invoked, and the other process termination steps per‐
       formed 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  unde‐
       fined.  On some systems (but not Linux), this can result in an infinite
       recursion; portable programs should not invoke exit(3) inside  a  func‐
       tion 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().

   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), dlopen(3), exit(3), on_exit(3)

COLOPHON
       This page is part of release 5.02 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/.



Linux                             2017-09-15                         ATEXIT(3)
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