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 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 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.kernel.org/doc/man-pages/reporting_bugs.html .