Popen in C++

simple_popen.cpp

#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

using namespace std;

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
	cerr << "please input command to execute" << endl;
	exit(1);
    }

    int stdinPipe[2] = {0};
    int stdoutPipe[2] = {0};
    int stderrPipe[2] = {0};
    const int READ_FD = 0, WRITE_FD = 1;

    if (pipe(stdinPipe) == -1)
    {
	cerr << "failed to create pipe" << endl;
	exit(1);
    }
    if (pipe(stdoutPipe) == -1)
    {
	cerr << "failed to create pipe" << endl;
	exit(1);
    }
    if (pipe(stderrPipe) == -1)
    {
	cerr << "failed to create pipe" << endl;
	exit(1);
    }

    pid_t pid = fork();
    if (pid == -1)
    {
	cerr << "failed to fork" << endl;
	exit(1);
    }
    else if (pid == 0) // child
    {
	// close useless fds
	close(stdinPipe[WRITE_FD]);
	close(stdoutPipe[READ_FD]);
	close(stderrPipe[READ_FD]);

	if (dup2(stdinPipe[READ_FD], STDIN_FILENO) == -1 ||
	    dup2(stdoutPipe[WRITE_FD], STDOUT_FILENO) == -1 ||
	    dup2(stderrPipe[WRITE_FD], STDERR_FILENO) == -1)
	{
	    cerr << "failed to dup2 fd" << endl;
	    exit(1);
	}
	else
	{
	    close(stdinPipe[READ_FD]);
	    close(stdoutPipe[WRITE_FD]);
	    close(stderrPipe[WRITE_FD]);
	}

	execvp(argv[1], argv + 1);

	// should not reach here
	cerr << "failed to exec" << endl;
	exit(1);
    }
    else // parent
    {
	// close useless fds
	close(stdinPipe[READ_FD]);
	close(stdoutPipe[WRITE_FD]);
	close(stderrPipe[WRITE_FD]);

	char c;
	while (read(stdoutPipe[READ_FD], &c, 1) == 1)
	{
	    cout << c;
	}

	cout << "child exit" << endl;
    }
    
    return 0;
}