Datatypes

MPI_CHAR

Definition

MPI_CHAR is an MPI_Datatype that represents a character type in MPI, it corresponds to a char in C. The difference with MPI_SIGNED_CHAR is that the latter is treated as the integral value, while MPI_CHAR is treated as a printable character. This is why MPI_SIGNED_CHAR can be used in reduction operations for instance while MPI_CHAR cannot.

Example

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

/**
 * @brief Illustrate how to communicate a character between 2 MPI processes.
 * @details This application is meant to be run with 2 MPI processes: 1 sender
 * and 1 receiver. The former sends a character to the latter, which prints it.
 **/
int main(int argc, char* argv[])
{
    MPI_Init(&argc, &argv);

    // Check that 2 MPI processes are used.
    int size;
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    if(size != 2)
    {
        printf("This application is meant to be run with 2 MPI processes.\n");
        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
    }

    // Get my rank and do the corresponding job.
    enum role_ranks { SENDER, RECEIVER };
    int my_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    switch(my_rank)
    {
        case SENDER:
        {
            // Sends the character
            char characterToSend = 'A';
            printf("[MPI process %d] I send character: '%c'.\n", my_rank, characterToSend);
            MPI_Ssend(&characterToSend, 1, MPI_CHAR, RECEIVER, 0, MPI_COMM_WORLD);
            break;
        }
        case RECEIVER:
        {
            // Receives the character
            char characterReceived;
            MPI_Recv(&characterReceived, 1, MPI_CHAR, SENDER, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            printf("[MPI process %d] I received character: '%c'.\n", my_rank, characterReceived);
            break;
        }
    }

    MPI_Finalize();

    return EXIT_SUCCESS;
}

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

/**
 * @brief Illustrate how to communicate a string between 2 MPI processes.
 * @details This application is meant to be run with 2 MPI processes: 1 sender
 * and 1 receiver. The former sends a string to the latter, which prints it.
 **/
int main(int argc, char* argv[])
{
    MPI_Init(&argc, &argv);

    // Check that 2 MPI processes are used.
    int size;
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    if(size != 2)
    {
        printf("This application is meant to be run with 2 MPI processes.\n");
        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
    }

    // Get my rank and do the corresponding job.
    enum role_ranks { SENDER, RECEIVER };
    int my_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    switch(my_rank)
    {
        case SENDER:
        {
            // Sends the string
            char stringToSend[] = "Hello world";
            printf("[MPI process %d] I send string: \"%s\".\n", my_rank, stringToSend);
            MPI_Ssend(stringToSend, strlen(stringToSend), MPI_CHAR, RECEIVER, 0, MPI_COMM_WORLD);
            break;
        }
        case RECEIVER:
        {
            // Receives the string
            char stringReceived[12];
            stringReceived[11] = '\0';
            MPI_Recv(stringReceived, 11, MPI_CHAR, SENDER, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            printf("[MPI process %d] I received string: \"%s\".\n", my_rank, stringReceived);
            break;
        }
    }

    MPI_Finalize();

    return EXIT_SUCCESS;
}