Forking N processes in chain - c

Question

I want to solve a certain problem and i can't figure it out how to do it properly. I have to create N processes in chain and after i finish making all of them, the initial process will random a number and write it in the pipe, the other processes read from the pipe the number, they randomize a number and substract the result from the number read, write it back to the pipe and so on. Here is what i've tried
#include <string.h>
#include <sys/types.h>
#include <stdlib.h>
#include <time.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#define P_READ 0
#define P_WRITE 1
void forker(int nprocesses, int** pipes, int fd[2])
{
pid_t pid;
int buf;
if(nprocesses > 0)
{
if ((pid = fork()) < 0)
{
perror("fork");
}
else if (pid == 0)
{
//Child
printf("Child %d created PID : %d , PPID : %d\n", nprocesses-1, getpid(), getppid());
int i = nprocesses - 1;
time_t t;
srand((int)time(&t) % getpid()); // get unique seed for every child
int r = (rand() % 11) + 10;
if (i==0) {
read(fd[P_READ], &buf, sizeof(int));
close(fd[P_READ]);
}else{
read(pipes[i-1][P_READ], &buf, sizeof(int));
close(pipes[i-1][P_READ]);
}
close(pipes[i][P_READ]);
buf -= r;
printf("%d|%d|%d|%d\n", buf, r, getpid(), getppid());
write(pipes[i][P_WRITE], &buf, sizeof(int)); // write
close(pipes[i][P_WRITE]);
printf("Child %d end\n", nprocesses-1);
}
else if(pid > 0)
{
forker(nprocesses - 1, pipes, fd);
}
}
}
int main (void)
{
int status = 0;
srand(time(NULL));
pid_t pid = getpid();
pid_t parent = getpid();
pid_t wpid;
int n, fd[2], buf;
printf("Please enter how many processes you want(between 6 and 15): ");
scanf("%d", &n);
while ( n < 6 || n > 15)
scanf("%d", &n);
int **pipes = (int **)malloc(n * sizeof(int*));
for(int i = 0; i < n; i++) pipes[i] = (int *)malloc(2 * sizeof(int));
printf("I'm parent - my pid is %d\n",pid);
pipe(fd);
for(int i=0; i<n; i++) {
if(pipe(pipes[i])) {
printf("pipe error");
return -1;
}
}
forker(n, pipes, fd);
if(parent == getpid()) {
close(fd[P_READ]);
buf = (rand() % 9001) + 1000;
printf("The initial number is %d created by process with pid : %d\n", buf, getpid());
write(fd[P_WRITE], &buf, sizeof(int));
close(fd[P_WRITE]);
}
while ((wpid = wait(&status)) > 0); // WAIT
if (pid == getpid()) printf("End of parent and my pid was %d\n", pid);
return 0;
}
The output looks something like this :
Please enter how many processes you want(between 6 and 15): 10
I'm parent - my pid is 3827
Child 9 created PID : 3828 , PPID : 3827
Child 8 created PID : 3829 , PPID : 3827
Child 7 created PID : 3830 , PPID : 3827
Child 6 created PID : 3831 , PPID : 3827
Child 5 created PID : 3832 , PPID : 3827
Child 2 created PID : 3835 , PPID : 3827
Child 3 created PID : 3834 , PPID : 3827
The initial number is 1625 created by process with pid : 3827
Child 1 created PID : 3836 , PPID : 3827
Child 4 created PID : 3833 , PPID : 3827
Child 0 created PID : 3837 , PPID : 3827
1609|16|3837|3827
Child 0 end
1589|20|3836|3827
1573|16|3835|3827
Child 2 end
1559|14|3834|3827
Child 3 end
1543|16|3833|3827
Child 4 end
1530|13|3832|3827
Child 5 end
Child 1 end
1511|19|3831|3827
Child 6 end
1498|13|3830|3827
Child 7 end
1488|10|3829|3827
Child 8 end
1470|18|3828|3827
Child 9 end
End of parent and my pid was 3827
The problem is that, i am not sure if the first number is randomed before the processes creation(but that's not the big issue here). The big issue is that the initial process creates all the child processes and it is not "in chain".

Answer 1

First fork you process N times, then generate the random number and pass it to other process.
So put the creation of the random number outside the loop for forking the main process