[SOLVED] problem with fork()ing multing child process in C

wch705 · 05-12-2011, 06:43 AM

i got basic knowledge about creating a single child from a parent using fork(). But when it comes into creating multiple children, i am simply stuck.
I am trying to create two processes from a parent and it would wait for both two processes to finish.
my attempt is as below

Code:

main()
{
	int pid,i;
	printf("let's start the process,and i am pid%d\n",getpid());
	for (i=0;i<=1;i++)
	{
		pid=fork();
		if ((pid>0))
		{
			wait(NULL);
			printf("i am the parent pid %d\n",getpid());
		}
		else if (pid==0)
		printf("i am the child pid %d\n",getpid());
	}
	return 0;
}

for some reasons, it came up with four processes.
the sample output:

Quote:

let's start the process,and i am pid2859
i am the child pid 2860
i am the child pid 2861
i am the parent pid 2860
i am the parent pid 2859
i am the child pid 2862
i am the parent pid 2859

could anyone point out the logic error?
thanks in advance.

dwhitney67 · 05-12-2011, 06:59 AM

Think about it... your child process continues within the for-loop. Since it appears that this is not your intent, then perhaps you should explicitly tell the child to exit.

theNbomr · 05-12-2011, 11:26 AM

Your child processes are doing exactly the same thing as the parent processes... which is to unconditionally fork() a child. You need to add logic to the top level, to determine whether or not to fork().
--- rod.

wch705 · 05-15-2011, 05:28 AM

after some days, i finally understood, thanks all for help