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



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

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 .



IEEE/The Open Group                  2017                            ATEXIT(3)
