fork(), could you explain!! Post: 302569233

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Top Forums Programming fork(), could you explain!! Post 302569233 by Praveen_218 on Sunday 30th of October 2011 10:36:03 AM

10-30-2011

Registered User

Quote:

Originally Posted by gabam

Dear friends,
We are learning UNIX system programming as part of our course. I came across this simple program, which the teacher didn't explain well enough. could you please explain this program fully

Code:

#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
int pid;
int status = 0;
if(pid = fork())
{
pid = wait(&status);
printf("%d\n",pid);
}
else
{
exit(status);
}
return 0;
}

And why does this program give an output of 912???
Thanks

Your program is calling printf(("%d\n",pid) from only one location (and from the if() block where its testing for the value of pid only after the expression pid = fork() is evaluated); so no mixture output, a simplest case of such fork() examples.

Who is executing that if() block ???. Its the parent (remind that fork() is a system call returns two times after a single call to it and it returns the parent (the callee to fork()) with the process id of the child it just created and a zero to that child. Hence that if() block is being executed by the parent only and its printing the process id it had received and collected in the variable pid of your program.

The output is just the process id of the child process created.

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