confusion about _exit

rajesh1978 · 06-18-2010, 05:43 AM

Hi,
I was reading difference between exit and _exit.

It tells that exit do the proper clean up but _exit does not.
exit flushes the buffer. So it is recomended that to use _exit in the child process.

My doubt is when we fork the memory space is also duplicated for child. Now child has it's own memory space. If I use exit in child then while exiting it will flush the buffer. It will not disturb the parent memory space(correct me if wrong).

So why there is a use of _exit.

and what sometime I see _exit(0) or some number inside the bracket. What does it mean

paulsm4 · 06-19-2010, 12:21 AM

"exit()" is the standard library call.

"exit()" is generally preferred.

The "status" parameter to both _exit() and exit() is the status value returned back to the operating system.

Here is the "man" page for "_exit()":

Code:

NAME
       _exit - terminate the current process

SYNOPSIS
       #include <unistd.h>

       void _exit(int status);

DESCRIPTION
       _exit terminates the calling process immediately. Any open
       file descriptors belonging to the process are closed;  any
       children  of the process are inherited by process 1, init,
       and the process's parent is sent a SIGCHLD signal.

       status is returned to the parent process as the  process's
       exit  status,  and  can be collected using one of the wait
       family of calls.

RETURN VALUE
       _exit never returns.

CONFORMING TO
       SVr4, SVID, POSIX, X/OPEN, BSD 4.3

NOTES
       _exit does not call any functions registered with the ANSI
       C atexit function and does not flush standard I/O buffers.
       To do these things, use exit(3).

SEE ALSO
       fork(2),   execve(2),   waitpid(2),   wait4(2),   kill(2),
       wait(2), exit(3)