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 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).

       +----------+---------------+---------+
       |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 functions registered functions calls _exit(2), then any remaining functions are not invoked, and the other  process  termina-
       tion steps performed 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
       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 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
");
       }

       int
       main(void)
       {
	   long a;
	   int i;

	   a = sysconf(_SC_ATEXIT_MAX);
	   printf("ATEXIT_MAX = %ld
", a);

	   i = atexit(bye);
	   if (i != 0) {
	       fprintf(stderr, "cannot set exit function
");
	       exit(EXIT_FAILURE);
	   }

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       _exit(2), dlopen(3), exit(3), on_exit(3)

COLOPHON

       This page is part of release 4.15 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)