Fork in C program
In this example, we will write a simple C program which will fork a child process. The "fork()" function will be used to do this.
fork() returns 0 to the child process and the child pid to the parent process. Our parent process and child process will count up to
ten. For process switching by operating system, we will observe in the output that the processes are not printing serially, rather
they are printing in turn.. Type in the following C program in your editor:
// forking.c
#include <stdio.h>
int main(void)
{
// Variable to hold the process id
int pid;
// Fork the process and get the process id in "pid"
pid = fork();
// Check the value of pid
if(pid == 0)
{
/* Child process:
* When fork() returns 0, we are in
* the child process.
* Here we count up to ten, one each second.
*/
int j;
for(j=0; j < 10; j++)
{
printf("child: %d\n", j);
// Force the process to sleep for one second
sleep(1);
}
_exit(0); /* Note that we do not use exit() because it is not
async-signal safe */
}
else if(pid > 0)
{
/* Parent process:
* Otherwise, we are in the parent process.
* Again we count up to ten.
*/
int i;
for(i=0; i < 10; i++)
{
printf("parent: %d\n", i);
// Force the process to sleep for one second
sleep(1);
}
}
else
{
/* Error handling. */
fprintf(stderr, "couldn't fork");
exit(1);
}
}
