fork-ex.c (download)


/* Includes */
#include /* Symbolic Constants */
#include /* Primitive System Data Types */
#include /* Errors */
#include /* Input/Output */
#include /* Wait for Process Termination */
#include /* General Utilities */

int main()
{
pid_t childpid; /* variable to store the child's pid */
int retval; /* child process: user-provided return code */
int status; /* parent process: child's exit status */

/* only 1 int variable is needed because each process would have its
own instance of the variable
here, 2 int variables are used for clarity */

/* now create new process */
childpid = fork();

if (childpid >= 0) /* fork succeeded */
{
if (childpid == 0) /* fork() returns 0 to the child process */
{
printf("CHILD: I am the child process!\n");
printf("CHILD: Here's my PID: %d\n", getpid());
printf("CHILD: My parent's PID is: %d\n", getppid());
printf("CHILD: The value of my copy of childpid is: %d\n", childpid);
printf("CHILD: Sleeping for 1 second...\n");
sleep(1); /* sleep for 1 second */
printf("CHILD: Enter an exit value (0 to 255): ");
scanf(" %d", &retval);
printf("CHILD: Goodbye!\n");
exit(retval); /* child exits with user-provided return code */
}
else /* fork() returns new pid to the parent process */
{
printf("PARENT: I am the parent process!\n");
printf("PARENT: Here's my PID: %d\n", getpid());
printf("PARENT: The value of my copy of childpid is %d\n", childpid);
printf("PARENT: I will now wait for my child to exit.\n");
wait(&status); /* wait for child to exit, and store its status */
printf("PARENT: Child's exit code is: %d\n", WEXITSTATUS(status));
printf("PARENT: Goodbye!\n");
exit(0); /* parent exits */
}
}
else /* fork returns -1 on failure */
{
perror("fork"); /* display error message */
exit(0);
}
}