Lecture 2 Part 1

Process Creation and getting ID

pid_t cpid = fork();

pid_t pid = getpid();   // Get current process ID
pid_t ppid = getppid();  // Get parent process ID

fork() return value:

0 : Child process
> 0 : Parent process, returns child's PID
-1 : Fork failed

Checking Process Status

Macro	Description
`WIFEXITED(status)`	Checks if the process exited normally
`WEXITSTATUS(status)`	Retrieves the exit status
`WIFSIGNALED(status)`	Checks if the process was killed by a signal
`WTERMSIG(status)`	Retrieves the signal number
`WIFSTOPPED(status)`	Checks if the process was stopped
`WSTOPSIG(status)`	Retrieves the stopping signal
`WIFCONTINUED(status)`	Checks if the process was resumed

if (WIFEXITED(status)) {
    printf("Child exited normally, status=%d\\n", WEXITSTATUS(status));
}

if (WIFSIGNALED(status)) {
    printf("Child killed by signal %d\\n", WTERMSIG(status));
}

if (WIFSTOPPED(status)) {
    printf("Child stopped by signal %d\\n", WSTOPSIG(status));
} else if (WIFCONTINUED(status)) {
    printf("Child continued\\n");
}

wait()

pid_t wait(int *status);

Blocks parent until any child process terminates.
Stores exit status in status.
Returns PID of terminated child or -1 on error (no child exists).

Return Value	Meaning
`> 0`	PID of the terminated child process
`-1`	No child processes or an error occurred

Example

int status;
pid_t pid = wait(&status);
if (pid > 0) printf("Child %d terminated\\n", pid);

waitpid()

pid_t waitpid(pid_t pid, int *status, int options);

Return Value	Meaning
`> 0`	PID of the terminated child process
`0`	Child process is still running (`WNOHANG` mode)
`-1`	Error (no child process or invalid call)