using Pipes create N child and send message to parent - c

Question

I'm trying to create n child with the same parent, and send the random number from child -> parent.
For now, I have a problem to send random 0/1 from child -> parent.
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<string.h>
#include<sys/wait.h>
int main()
{
pid_t pids[10];
int i;
int n = 10;
/* Start children. */
for (i = 0; i < n; ++i) {
if ((pids[i] = fork()) < 0) {
perror("fork");
abort();
} else if (pids[i] == 0) {
// printf("I am a child with id %d and my parent %d\n",getpid(),getppid());
int random = rand() % 2;
printf("\nChild send random: %d\n",random);
write(pids[1], &random, sizeof(random));
exit(0);
}
else{
int ran;
read(pids[0], &ran, sizeof(ran)); // read from child
printf("\nParent Received: %d\n", ran);
}
}
wait(NULL);
}

Answer 1

The problems are:
first, read and write don't want a pid like first argument but a file descriptor and second, for passing something between two processes you should use a IPC mechanism like pipes:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <sys/wait.h>
#include <time.h>
int main()
{
pid_t pids[10];
int _pipe[2];
int i;
int n = 10;
int random;
srand(time(NULL));
/* Start children. */
for (i = 0; i < n; ++i) {
//printf("%d\n",i);
pipe(_pipe);
if ((pids[i] = fork()) < 0) {
perror("fork");
abort();
} else if (pids[i] == 0) { // Child
random = rand() % 2;
char str[2];
sprintf(str,"%d",random);
//printf("\nChild send random: %d\n",random);
close(_pipe[0]);
write(_pipe[1], str, sizeof(str));
printf("Pipe sended: %s\n",str);
exit(0);
}
else{ // Parent
char string[1];
close(_pipe[1]);
read(_pipe[0],string,sizeof(string)); // read from child
printf("pipe received: %s\n",string);
//printf("\nParent Received: %d\n", ran);
}
}
wait(NULL);
}