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SubjectRe: fork() Problem?
On Wed, 5 May 1999, Yavuz Selim Komur wrote:

> On Tue, 4 May 1999, David Miller wrote:
>
> >
> > You do not initialize the "status" variable passed to wait(), this is
> > probably why it crashes on SunOS. "status" could contain anything,
> > any value, and probably it contains garbage or a wild pointer.
>
> Execuse me. I didn't well defined my problem. SegFault? ignore it.
>
> Problem is sequence error.
>
> if (pid = fork())
^^^^________ logical test of an assignment? This will always
be true!
if((pid = fork()) != 0) or
if((pid = fork()))
You need to make the assignment first, then
test for non-zero.


> printf("Main Program");
> else
> printf("Child Program");
>
> it's clear?

No, also if you want a defined order in which stuff is printed either
do fprintf(stderr, "whatever"); or printf("whatever"); fflush(stdout);

Standard output is buffered.

This works fine, and in the correct order.

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

int main(void);
int main()
{
pid_t pid;
int status;
switch((pid = fork()))
{
case 0: /* Child */
fprintf(stderr,"Child (%ld)\n", getpid());
exit(123);
case -1:
fprintf(stderr, "Error with fork()\n");
exit(2);
default: /* Parent */
fprintf(stderr, "Parent waits for child (%ld) status\n", pid);
wait(&status);
fprintf(stderr, "Child's exit status was %d\n", status >> 8);
}
return 0;
}

Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.2.6 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.

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