C程序中的多个fork（）

Question

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
    pid_t pid1, pid2, pid3, pid4;
    pid1=fork();

    if (pid1!=0) {
        pid2=fork();
        pid3=fork(); 
    }else { 
        pid4=fork(); 
    } 
    return 0;
}

Hello, The following code executes 4 forks. At first the original process(Lets call it P0) executes the "pid1=fork()" and creates a child(Lets call it P1). Then the original process again executes the pid2=fork() and creates another child(Let's call it P2). Then both the P2 and the P0 execute the "pid3=fork()". So the P0 creates a third child(Call it P3) and the P2 becomes a parent and creates a child(Call it P4). And in the end, in the else statement the very first child(P1) creates a child(P5). So the tree is like :

                  P0
              P1   P2   P3
            P5      P4

My question is: Am i right or not? Thanks in advance.

Answer 1

My question is: Am i right or not?

Yes.

As Paul R says in the comments, try putting some printf's in. For example after

pid1 = fork()

Try putting

printf("pid %d: pid1 = fork(), result = %d\n", getpid(), pid1);

getpid() gets the pid of the current process.

Answer 2

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
pid_t pid1, pid2, pid3, pid4;
printf("PID=%d, PPID=%d.\n", getpid(), getppid());
pid1=fork();

if (pid1!=0) {
 pid2=fork();
 printf("PID=%d, PPID=%d.\n", getpid(), getppid());
 pid3=fork(); 
 printf("PID=%d, PPID=%d.\n", getpid(), getppid());
}else { 
  pid4=fork();
  printf("PID=%d, PPID=%d.\n", getpid(), getppid()); } 
return 0;
}

I added some printfs and i print the process id and the parent process id but everyone has the same parent. Is it because the original process finishes first? i get this output