pipe_average.cpp

#include <sys/wait.h>
#include <unistd.h>
#include <vector>
#include <iostream>
#include <string>
#include <array>
#include <algorithm>

bool pipeRead(int pipe, int& value)
{
	int readed = 0;
	readed = read(pipe, &value, sizeof(value));
	if (readed == -1)
	{
		perror("Error reading pipe.");
		exit(EXIT_FAILURE);
	}
	else
		if (readed == 0)
			return false;
	return true;
}

void pipeWrite(int pipe, int value)
{
	if (write(pipe, &value, sizeof(value)) == -1)
	{
		perror("Error writing pipe.");
		exit(EXIT_FAILURE);
	}
}


std::vector<std::array<int, 2>> createPipes(int count)
{
	std::vector<std::array<int, 2>> pipes;
	for (int i = 0; i < count; ++i)
	{
		std::array<int, 2> newPipe;
		int* data = newPipe.data(); // data is the pointer to a 2-element table of int
		if (pipe(newPipe.data()) == -1)
		{
			perror("Error creating pipe.");
			exit(EXIT_FAILURE);
		}
		pipes.push_back(newPipe);
	}
	return pipes;
}


// TODO add second child processy, that will be a proxy to pass the numbers and that will count the average (displayed after receiving all the numbers)

int main(int argc, char* argv[])
{
	auto pipes = createPipes(2);

	if (fork() == 0)
	{
		// child
		close(pipes[0][0]);
		close(pipes[1][0]);
		close(pipes[1][1]);
		int value;
		do
		{
			std::cin >> value;
			if (value > 0)
				pipeWrite(pipes[0][1], value);
		} while (value > 0);
		close(pipes[0][1]);
	}
	else
	{
		// parent
		close(pipes[0][1]);
		close(pipes[1][0]);
		close(pipes[1][1]);
		int value;
		while (pipeRead(pipes[0][0], value))
			std::cout << "(Parent:" << getpid() << "):" << value << "\n";
		close(pipes[0][0]);
	}
	return 0;
}