# atexit

## 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.
    


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