atexit(3posix) [posix man page]

ATEXIT(P)						     POSIX Programmer's Manual							 ATEXIT(P)

NAME

       atexit - register a function to run at process termination

SYNOPSIS

       #include <stdlib.h>

       int atexit(void (*func)(void));

DESCRIPTION

       The atexit() function shall register the function pointed to by func, to be called without arguments at normal program termination. At nor-
       mal program termination, all functions registered by the atexit() function shall be called, in the reverse  order  of  their  registration,
       except that a function is called after any previously registered functions that had already been called at the time it was registered. Nor-
       mal termination occurs either by a call to exit() or a return from main().

       At least 32 functions can be registered with atexit().

       After a successful call to any of the exec functions, any functions previously registered by atexit() shall no longer be registered.

RETURN VALUE

       Upon successful completion, atexit() shall return 0; otherwise, it shall return a non-zero value.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The functions registered by a call to atexit() must return to ensure that all registered functions are called.

       The application should call sysconf() to obtain the value of {ATEXIT_MAX}, the number of functions that can be registered. There is no  way
       for an application to tell how many functions have already been registered with atexit().

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exit() , sysconf() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
       and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								 ATEXIT(P)

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 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 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.1-2001 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 functions 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
");
       }

       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), exit(3), on_exit(3)

COLOPHON

       This  page is part of release 3.27 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)