#include <stdlib.h> int atexit(void (*function)(void));
The same function may be registered multiple times: it is called once for each registration.
POSIX.1-2001 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered. The actual limit supported by an implementation can be obtained using sysconf(3).
When a child process is created via fork(2), it inherits copies of its parent's registrations. Upon a successful call to one of the exec(3) functions, all registrations are removed.
If one of the functions registered functions calls _exit(2), then any remaining functions are not invoked, and the other process termination steps performed by exit(3) are not performed.
POSIX.1-2001 says that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered using atexit(3)) is undefined. On some systems (but not Linux), this can result in an infinite recursion; portable programs should not invoke exit(3) inside a function registered using atexit(3).
The atexit() and on_exit(3) functions register functions on the same list: at normal process termination, the registered functions are invoked in reverse order of their registration by these two functions.
POSIX.1-2001 says that the result is undefined if longjmp(3) is used to terminate execution of one of the functions registered atexit().
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void
bye(void)
{
printf("That was all, folks\n");
}
int
main(void)
{
long a;
int i;
a = sysconf(_SC_ATEXIT_MAX);
printf("ATEXIT_MAX = %ld\n", a);
i = atexit(bye);
if (i != 0) {
fprintf(stderr, "cannot set exit function\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}