_onexit -- Record Termination Function

Format

#include <stdlib.h>
onexit_t _onexit(onexit_t func);

Language Level: Extension
_onexit records the address of a function func to call when the program ends normally. Successive calls to _onexit create a stack of functions that run in a last-in, first-out order. The functions passed to _onexit cannot take parameters.

You can record up to 32 termination functions with calls to _onexit and atexit. If you exceed 32 functions, _onexit returns the value NULL.

Note: For portability, use the ANSI/ISO standard atexit function, which is equivalent to _onexit.

Return Value
If successful, _onexit returns a pointer to the function; otherwise, it returns a NULL value.

Example
This example specifies and defines four distinct functions that run consecutively at the completion of main.

#include <stdio.h>
#include <stdlib.h>
int fn1(void)
{
   printf("next.\n");
   return 0;
}
int fn2(void)
{
   printf("run ");
   return 0;
}
int fn3(void)
{
   printf("is ");
   return 0;
}
int fn4(void)
{
   printf("This ");
   return 0;
}
int main(void)
{
   _onexit((onexit_t)fn1);
   _onexit((onexit_t)fn2);
   _onexit((onexit_t)fn3);
   _onexit((onexit_t)fn4);
   printf("This is run first.\n");
   return 0;
   /***********************************
      The output should be:
      This is run first.
      This is run next.
   ***********************************/
}



abort -- Stop a Program
atexit -- Record Program Termination Function
exit -- End Program
_exit -- End Process
<stdlib.h>