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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  corresponding
       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 normal
       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
       further exit() processing, it must call the  _exit()  function  or  the
       _Exit()  function  or one of the functions which cause abnormal process
       termination.
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 Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal 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 Standard
       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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           ATEXIT(3P)