exit and _exit

Learn the difference between exit and _exit.

exit and _exit

exit(status) terminates the process. It first calls functions registered with atexit, then flushes stdio buffers, and finally exits to the kernel.

_exit(status) does a direct kernel exit; it does not flush buffers or call atexit functions. After fork, using _exit in the child before exec is safer; because stdio buffers may be shared with the parent.

atexit functions

atexit(fn) registers a function to be called when the process exits normally. When exit is called, these functions run in reverse order of registration.

You can register up to 32 functions (varies across systems). _exit or signal termination does not call atexit functions. So registering cleanup with atexit is a safe approach: it works with both return and exit.

Exercise Cleanup with atexit

Write void farewell(void) containing printf("goodbye\n");. In main, register it with atexit(farewell);. Print printf("merhaba\n"); and exit with exit(0);.

Show example solution

#include <stdio.h>
#include <stdlib.h>

void farewell(void) {
    printf("goodbye\n");
}

int main(void) {
    atexit(farewell);
    printf("merhaba\n");
    exit(0);
}

Test yourself

Match exit functions

exit

Flushes buffers
_exit

Exits immediately
atexit

Registers function
return

Ends function
What is the difference between _exit and exit?
- _exit returns
- exit is faster
- _exit does not flush buffers
- exit sends a signal
Show answer

_exit does not flush buffers — _exit does a direct kernel exit without flushing buffers.

atexit registration

atexit(____);
exit(0);

Show answer

atexit(farewell);
exit(0);

Next lesson: Summary - Process management

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