`atexit`

Article
10/26/2022

Processes the specified function at exit.

Syntax

int atexit(
   void (__cdecl *func )( void )
);

Parameters

func
Function to be called.

Return value

atexit returns 0 if successful, or a nonzero value if an error occurs.

Remarks

The atexit function is passed the address of a function func to be called when the program terminates normally. Successive calls to atexit create a register of functions that are executed in last-in, first-out (LIFO) order. The functions passed to atexit can't take parameters. atexit and _onexit use the heap to hold the register of functions. Thus, the number of functions that can be registered is limited only by heap memory.

The code in the atexit function shouldn't contain any dependency on any DLL that could have already been unloaded when the atexit function is called.

To generate an ANSI-conformant application, use the ANSI-standard atexit function (rather than the similar _onexit function).

Requirements

Routine	Required header
`atexit`	`<stdlib.h>`

Example

This program pushes four functions onto the stack of functions to be executed when atexit is called. When the program exits, these programs are executed on a last in, first out basis.

// crt_atexit.c
#include <stdlib.h>
#include <stdio.h>

void fn1( void ), fn2( void ), fn3( void ), fn4( void );

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

void fn1()
{
   printf( "next.\n" );
}

void fn2()
{
   printf( "executed " );
}

void fn3()
{
   printf( "is " );
}

void fn4()
{
   printf( "This " );
}

This is executed first.
This is executed next.