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.1‐2017 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.1‐2017, <stdlib.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .