onexit-onexit-m.md

description	title	ms.date	api_name	api_location	api_type	topic_type	f1_keywords	helpviewer_keywords	ms.assetid
Learn more about: _onexit, _onexit_m	_onexit, _onexit_m	11/04/2016	_onexit _onexit_m	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll	DLLExport	apiref	_onexit onexit_m onexit _onexit_m	onexit function registry, registering exit routines _onexit_m function onexit_m function _onexit function registering exit routines registering to be called on exit	45743298-0e2f-46cf-966d-1ca44babb443

_onexit, _onexit_m

Registers a routine to be called at exit time.

Syntax

_onexit_t _onexit(
   _onexit_t function
);
_onexit_t_m _onexit_m(
   _onexit_t_m function
);

Parameters

function
Pointer to a function to be called at exit.

Return value

_onexit returns a pointer to the function if successful or NULL if there's no space to store the function pointer.

Remarks

The _onexit function is passed the address of a function (function) to be called when the program terminates normally. Successive calls to _onexit create a register of functions that are executed in LIFO (last-in-first-out) order. The functions passed to _onexit can't take parameters.

In the case when _onexit is called from within a DLL, routines registered with _onexit run when the DLL is unloaded, after DllMain is called with DLL_PROCESS_DETACH.

_onexit is a Microsoft extension. For ANSI portability, use atexit. The _onexit_m version of the function is for mixed mode use.

Requirements

Routine	Required header
_onexit	<stdlib.h>

For more compatibility information, see Compatibility.

Example

// crt_onexit.c

#include <stdlib.h>
#include <stdio.h>

/* Prototypes */
int fn1(void), fn2(void), fn3(void), fn4 (void);

int main( void )
{
   _onexit( fn1 );
   _onexit( fn2 );
   _onexit( fn3 );
   _onexit( fn4 );
   printf( "This is executed first.\n" );
}

int fn1()
{
   printf( "next.\n" );
   return 0;
}

int fn2()
{
   printf( "executed " );
   return 0;
}

int fn3()
{
   printf( "is " );
   return 0;
}

int fn4()
{
   printf( "This " );
   return 0;
}

Output

This is executed first.
This is executed next.

See also

Process and environment control
atexit
exit, _Exit, _exit
__dllonexit