ATEXIT(3P)						     POSIX Programmer's Manual							ATEXIT(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       atexit -- register a function to run at process termination

SYNOPSIS

       #include <stdlib.h>

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

DESCRIPTION

       The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here
       and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

       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.
       Normal 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().

       Since  the  behavior  is undefined if the exit() function is called more than once, portable applications calling atexit() must ensure that
       the exit() function is not called at normal process termination when all functions registered by the atexit() function are called.

       All functions registered by the atexit() function are called at normal process termination, which occurs by a call to the  exit()  function
       or a return from main() or on the last thread termination, when the behavior is as if the implementation called exit() with a zero argument
       at thread termination time.

       If, at normal process termination, a function registered by the atexit() function is called and a portable application needs to	stop  fur-
       ther exit() processing, it must call the _exit() function or the _Exit() function or one of the functions which cause abnormal process ter-
       mination.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exec, exit(), sysconf()

       The Base Definitions volume of POSIX.1-2008, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								ATEXIT(3P)