_onexit, _onexit_m


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Registers a routine to be called at exit time.


_onexit_t _onexit(  
   _onexit_t function  
_onexit_t_m _onexit_m(  
   _onexit_t_m 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 is no space to store the function pointer.


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 cannot take parameters.

In the case when _onexit is called from within a DLL, routines registered with _onexit run on a DLL's unloading 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.


Routine Required header
_onexit <stdlib.h>

For more compatibility information, see Compatibility in the Introduction.


// 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;  


This is executed first.  
This is executed next.  

.NET Framework Equivalent


See Also

Process and Environment Control
exit, _Exit, _exit