// hello_world.cc
//
// Hello World Program

#include <cstdlib>
#include <iostream>
#include <fstream>
#include "mpi.h"

using namespace std;

int main(void) {

  MPI::Init();  // initialisiere MPI

  int rank=MPI::COMM_WORLD.Get_rank();  // ascertain own rank
  int size=MPI::COMM_WORLD.Get_size();  // and number of processes

  const int max_proc_name_length=MPI::MAX_PROCESSOR_NAME+1;
  int proc_name_length;
  char *proc_name;
  try {
    proc_name=new char[max_proc_name_length];
  } 
  catch (bad_alloc &e) {  // not enough memory
    MPI::COMM_WORLD.Abort(EXIT_FAILURE);  // terminate all processes
  }
  MPI::Get_processor_name(proc_name, proc_name_length);  // which hostname?
  proc_name[proc_name_length]='\0';
  
  if (rank==0) {  // rank 0 is indicated
    ofstream out("hello_world.out");  // create output file
    if (!out)  // error => terminate processs
      MPI::COMM_WORLD.Abort(EXIT_FAILURE);
    // Receive status reports of other ranks and write to file 
    for (int i=0; i<size; ++i) {
      // Receive string and write to file
      if (i>0)
	MPI::COMM_WORLD.Recv(proc_name, max_proc_name_length, MPI::CHAR, i, 0);
      out << "Hello World! My rank is " << i << " of " << size << ". "
	  << "I am running on " << proc_name << "." << endl;
    }
  } else
    // Send string
    MPI::COMM_WORLD.Send(proc_name, proc_name_length+1, MPI::CHAR, 0, 0);

  MPI::Finalize();  // terminate MPI

  return EXIT_SUCCESS;
}