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  im-
       plementation 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  at-
       tributes(7).

       +----------+---------------+---------+
       |Interface | Attribute     | Value   |
       +----------+---------------+---------+
       |atexit()  | 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 in-
       voked 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 4.16 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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