C++ dup2 and execl - c++

Question

I am working on an assignment and I need to create pipes so that other programs handle different functions. I am able to pipe through the command line no problem, thats easy. However using dup2 and execl have been tricky for me. At one point I was able to get output from one part of my program but it wasn't reading anything in from another part.
here is what i have:
pipeline.cpp
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <cstdlib>
#include <iostream>
#include <cctype>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include<iostream>
#include<cstdlib>
#include<unistd.h>
#include<iomanip>
#include <sys/wait.h>
using namespace std;
int main(int argc, char *argv[])
{
int number = atoi(argv[1]);
int x2ypipe[2];
pipe(x2ypipe);
if(x2ypipe==0){
cout<<"ERROR:"<<errno<<endl;
}
pid_t xchild =fork();
if(xchild==0){
dup2(x2ypipe[1],STDOUT_FILENO);
close(x2ypipe[0]);
close(x2ypipe[1]);
execl("./part1.cpp","part1.cpp", (char *)NULL);
}
pid_t ychild =fork();
if(ychild==0){
dup2(x2ypipe[0],STDIN_FILENO);
close(x2ypipe[0]);
close(x2ypipe[1]);
execl("./part2.cpp", "part2.cpp", (char *)NULL);
}
close(x2ypipe[0]);
close(x2ypipe[1]);
wait(NULL);
wait(NULL);
part1.cpp
#include<iostream>
#include<cstdlib>
#include<unistd.h>
#include<iomanip>
using namespace std;
int main(int argc, char *argv[])
{
int number = atoi(argv[1]);
for (int k = 1; k <= 9; k++)
{
cout << k << " " << flush;
sleep(1);
}
return 0;
}
part2.cpp
#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <iomanip>
using namespace std;
int main()
{
int number;
while (cin >> number)
{
cout << 2 * number - 1 << " " << flush;
}
return 0;
}
Ok so pipeline.cpp : forks twice and creates a pipe between the two children. Then each use excel to replace its process with the programs part1 and part2. So my understanding is that part1 program would run and anything it outputs will be picked up by the second child which runs part2 and from there part two would output normally since it's output descriptor wasn't changed. Am I missing or misusing something here?

Answer 1

I noticed a couple of things:
You're not passing the number to the part1 process when you exec it
You're not checking for failure from execl() or any of the other OS functions
I think once you do these two things, you'll find out what the real problem is. I won't just tell you what the answer is, because it's worthwhile learning how to diagnose such problems yourself. (I was able to run your code successfully with only minor modifications. The problem does not lie in how you're handling the pipes and file descriptors.)

Answer 2

I think you need to return 0; after your exec calls. But I am even more lost than you it seems.