Programming

I followed your advice on checking the returned value of read () and write (), read returns 4 bytes, which is the same as what write() returns, I believe that means I only get the chance to read the input from the child that finishes last, as he overwrites the pipe ?

At this point I only see 2 solutions for the problem, the one I already solved, and having a pipe for every child like shamrock suggested(an array of pipes maybe ?), will try the sham's proposal.

But if you are allowed to call read only once in the parent then it wont work as my solution requires 2 reads. Going over your posted code it looks like you start with one parent then fork creating a child which then forks itself creating another child...so you end up having a parent a child and a grandchild. Is that how you are supposed to approach it as that simplifies things and makes it completely doable with a single read in the parent.

If you follow the code more closely you'll notice that it's only the parent that calls fork(), so what i have is a parent with n children processes.

Easy way to check this, do:

int pid = getppid(); // pid = parent's pid
printf ("pid = %d\n", pid);

inside of if (pid [i] == 0) { } , you'll get the same parent pid for each of the n children.

Code:

int aux[nr_proc]

you should give this a fixed number not a variable. sizeof() is set at compile-time and knows nothing about variable-size arrays. I think sizeof() is only giving you 4.

I tried to do that, it still returns 4, which is also the size of an int in my debian.

In your code, you are creating pipe inside loop

Code:

for (i = 0; i < nr_proc; i++) {
     pipe (fd);

So you are losing data of previous child, try to keep it above for loop and try...

I can't believe how simple that was, it works now. You have my sincere gratitude !