#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <mpi.h>


int main(int argc, char **argv)
{
    char *env_hostname;
    char hostname[255];
    int myrank, size;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    env_hostname = getenv("HOSTNAME");
    if (NULL != env_hostname) {
        printf("Processor %d of %d on $HOSTNAME %s: Hello World\n",
               myrank, size, env_hostname);
    } else {
        printf("Processor %d of %d on $HOSTNAME NULL: Hello World\n",
               myrank, size);
    }
    if (0 == gethostname(hostname, 255)) {
        printf("Processor %d of %d on host %s: Hello World\n",
               myrank, size, hostname);
    }

    MPI_Finalize();

    exit(0);
}