How can I use atexit() function to cleanup function call?

Question

I am using atexit() function inside my code to cleanup function call, but it's not working.

#include<stdio.h>
void ftn(void)
{
    printf(" Function called --> exit\n");
    return;
}
int main(void)
{
    int x = 0;
    atexit(ftn);
    for(;x<0xffffff;x++);
    _exit(0);
}

Any help regarding this will be appreciated.

You should mostly call `_exit` ever when in a child process after a `fork` and you must not call the original cleanup code because the clean up belongs to the parent. — Antti Haapala -- Слава Україні, May 29 '19 at 07:31

abbasi_ahsan · Accepted Answer · 2019-05-29T07:24:26.580

This behavior of atexit() function is due to the use of function _exit(). This function does not call the clean-up functions like atexit() etc. If atexit() is required to be called then exit() or ‘return’ should be used instead of _exit().

As:

#include<stdio.h>
void ftn(void)
{
    printf(" Function called --> exit\n");
    return;
}
int main(void)
{
    int x = 0;
    atexit(ftn);
    for(;x<0xffffff;x++);
    exit(0);
}

score 2 · Answer 2 · answered May 29 '19 at 07:18

_exit close the program without calling at exit methods Further reading.

Thus, use exit(0); instead of _exit(0);

#include<stdio.h>
void ftn(void)
{
    printf(" Function called --> exit\n");
    return;
}
int main(void)
{
    int x = 0;
    atexit(ftn);
    for(;x<0xffffff;x++);
    exit(0);
}

Sourav Ghosh · Answer 3 · 2019-05-29T07:26:52.437

Quoting the man page for _exit()

The _Exit() and _exit() functions shall not call functions registered with atexit() nor any registered signal handlers. Whether open streams are flushed or closed, or temporary files are removed is implementation-defined. Finally, the calling process is terminated with the consequences described below.

So what you're seeing is expected behavior.

That said, you should include unistd.h (for _exit())and stdlib.h (for atexit()) headers for including the prototype.

If you want the functions registered by atexit() to be invoked, you should call exit() instead.

The exit() function shall first call all functions registered by atexit(), in the reverse order of their registration, [....]

How can I use atexit() function to cleanup function call?

3 Answers3