#include <unistd.h>
#include <iostream>

// Headers for wait
#include <sys/types.h>
#include <sys/wait.h>

using namespace std;


#define READ_PIPE 0
#define WRITE_PIPE 1

int main( int argc, char * argv[] )
{
  cout << "Original Process: PID=" << getpid() << " PPID=" << getppid() << endl;

  // The message to send to the child
  string message = "Hello from the parent!";

  // Create a pipe to be used to talk to the child
  // Two sides of the pipe are created, a read side and a write side. The parent
  // program will send data to the child, and the child will display it to the
  // screen.
  int pipeFD[2];
  if( pipe(pipeFD) == -1 ) {
    cout << "Error, cannot create pipe" << endl;
    return 0;
  }

  int pid = fork();
  if( pid != 0 ) {
    // This is the parent process
    cout << "Parent Process: PID=" << getpid() << " PPID=" << getppid() << endl;

    // We must close the side of the pipe that we do not need
    close( pipeFD[READ_PIPE] );

    // Send the message to the child
    write( pipeFD[WRITE_PIPE], message.c_str(), message.length() );

    // Wait for the child to finish before exiting
    int status;
    pid = wait( &status );

    // Close the remaining pipe
    close( pipeFD[WRITE_PIPE] );
  }
  else {
    // This is the child process
    cout << "Child Process: PID=" << getpid() << " PPID=" << getppid() << endl;

    // We must close the side of the pipe that we do not need
    close( pipeFD[WRITE_PIPE] );

    // Read the message from the parent. We have to know how long the message
    // is going to be
    int length = message.length();
    char longMessage[256];
    read( pipeFD[READ_PIPE], longMessage, length );

    // Display the message to the screen
    cout << "Child Process: Received Message..." << endl << longMessage << endl;

    // Close the remaining pipe
    close( pipeFD[READ_PIPE] );
  }

  cout << "Terminating Process PID=" << getpid() << endl;
  return 0;
}