creating child process from child [closed] - c

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I'm not entirely sure when I'm using fork() for child process process
there is child process creating other child process even though child process which is parent for other process (has status 0)?
#include <stdio.h>
int main()
{
printf("new proces");
if (fork() == 0) {
printf("child parent");
if (fork() == 0)
printf("child child");
}
printf("\n");
}
I'm confused because I'm not sure that when child proces invokes fork() it creates new proces or not?
because in this code
#include<stdio.h>
int main(){
printf(" do ");
if(fork()!=0) printf("ma ");
if(fork()==0) printf("to \n");
else printf("\n");
}
i have result like in this code there is child parent process which doesn't have status 0 and I don't know why beacuse it is child process of first parent process
do ma
do ma to
do to
do
not like this
do ma
do do to
to
child process invoking fork doesn't return 0 beause I have two ma not only one and i don't have idea why

Answer 1

Yes. The process creates a child, which then creates another child, becoming it's parent.
You can differentiate child and parent by using fork return number. From fork:
On success, the PID of the child process is returned in the parent,
and 0 is returned in the child. On failure, -1 is returned in the parent,
no child process is created, and errno is set appropriately.
You need to check fork() return value. If it returns 0, that means this process is a child. If it returns value greater then 0, then this process is the parent and the returned value is the childs process id.
Take a look at this program. I have added usleep calls to make processes print one after another:
#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
int main(){
// lets create a family!
pid_t grandpa_pid = getpid();
pid_t child_pid;
if ((child_pid = fork()) == 0){
pid_t parent_pid = getpid();
pid_t child_child_pid;
if ((child_child_pid = fork()) == 0) {
usleep(200);
printf("I am child and I will write third. My pid is %d, %d is my parent and %d is my parents parent, so my grandpa.", getpid(), parent_pid, grandpa_pid);
} else {
usleep(100);
// parent_pid = getpid()
printf("I am parent and I will write second. My pid is %d, %d is my child and %d is my parent.", getpid(), child_child_pid, grandpa_pid);
}
} else {
// grandpa_pid == getpid()
printf("I am grandpa and I will write first. My pid is %d and %d is my child.", getpid(), child_pid);
}
printf("\n");
}
Which produces the following output:
I am grandpa and I will write first. My pid is 5 and 6 is my child.
I am parent and I will write second. My pid is 6, 7 is my child and 5 is my parent.
I am child and I will write third. My pid is 7, 6 is my parent and 5 is my parents parent, so my grandpa.