MPIHelloWorldSendAndReceive

From Parawiki

MPIHelloWorldSendAndReceive.c

//compilation: 
//$ mpicc -o program MPIHelloWorldSendAndReceive.c
//$ mpirun -np number_of_processes program
//If you want to use multiple processors you have to use lamboot before! 
//if the mpi.h cannot be found by the compiler, try to locate mpi.h:
//open a terminal and: $ locate mpi.h
//and then include by giving the whole path to mpi.h
//in this example there are two distict send and receive operations
//distinction is made by tags and status
#include <stdio.h>
#include <string.h>
#include "mpi.h"        
int main(int argc, char* argv[]) {
	int rank, size;			//process rank and number of processes
	int source, destination;	//the sender and the receiver
	int tag_message = 0; 		//tag for send/receive
	int tag_rank = 1;      		//tag for send/receive
	MPI_Status status_message; 	//stores status for MPI_Recv statements
	MPI_Status status_rank;  	//stores status for MPI_Recv statements	
	char message[20];	  	//display messages to send/receive
	MPI_Init(&argc, &argv); 	//MPI initialize
	MPI_Comm_size(MPI_COMM_WORLD, &size); //get the number of processes
	MPI_Comm_rank(MPI_COMM_WORLD, &rank); //get the process ranks
	//process0 is going to receive messages from other processes
	//each process writes "hello world" to a message and sends it to the receiver process
	//each process sends its rank
	//process0, displays the message and the corresponding rank number
	if (rank!=0) {
		destination = 0; 		//set the receiver process process0
		strcpy(message, "Hello World!");
		//send the message to process0, use tag_message 
        	MPI_Send(message, strlen(message)+1, MPI_CHAR, destination, tag_message, MPI_COMM_WORLD); 
		//send the rank to process0, use tag_rank
		MPI_Send(&rank, 1, MPI_INT, destination, tag_rank, MPI_COMM_WORLD); 
	} 
	else 
        	for(source = 1; source < size; source++){
			//process0 receives the message by using tag_message and  status_message
        		MPI_Recv(message, 100, MPI_CHAR, source, tag_message,  MPI_COMM_WORLD, &status_message); 
			//process0 receives the rank by using tag_rank and  status_rank
			MPI_Recv(&rank, 1, MPI_INT, source, tag_rank,  MPI_COMM_WORLD, &status_rank); 
			printf("This \"%s\"", message);
			printf("is sent from process %d of %d to process %d\n",  rank, size, destination);
		}
	MPI_Finalize(); //MPI finalize
	return 0;
}