How can I see the actual value in memory of a pointer, C++?

Question

Ok, I took this code from some exercises of Intel for MKL, the code creates 2 matrixes 4x4 and multiplies them by using "cblas_dgemm". As result, the code gives you the time the program took to multiply those matrixes, so, I comprehend in some way the code, however, I dont know how to SEE the elements of the matrices A,B, and C(the result of the multiplication). Can you provide mee some code to print the values(elements of the matrices) of A,B and C? Any hint would be appreciated, thanks.

This the part in which the matrices are populated.

printf("Initialize the matrices\n");
    init_matrix<double>(A, m, k);
    init_matrix<double>(B, k,n);
    printf("Initialize the results matrix to 0s\n");
    init_matrix<double>(C, m,n,0);

This is the complete code. I would like to do something like cout<<C[i][j] in a for loop to print the elements of the matrices before and after the multiplication(cblas_dgemm).

#define min(x,y) (((x) < (y)) ? (x) : (y))
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include "mkl.h"
#include <chrono>

using namespace std;
using namespace std::chrono;



template <class T>
void init_matrix(T* a, int m, int n, T value = 1) {
    for (int i = 0;i < m * n;i++) {
        if (value == 1) {
            a[i] = (T)(rand() % 100);
        }
        else {
            a[i] = 0;
        }
    }
}

auto get_time() {
    return std::chrono::high_resolution_clock::now();
}

double random(float i, float j) {
    return ((float(rand()) * j) / float((RAND_MAX)) * i);
    }



int main()
{
    int m, n, k;
    m = 4, k = 4, n = 4;
    
    double* A, * B, * C;
    
    double alpha, beta; 

    alpha = 1.0; beta = 0.0;
    printf(" Allocating memory for matrices aligned on 64-byte boundary for better \n"
        " performance \n\n");

    A = (double*)mkl_malloc(m * k * sizeof(double), 64);
    B = (double*)mkl_malloc(k * n * sizeof(double), 64);
    C = (double*)mkl_malloc(m * n * sizeof(double), 64);

    printf("Initialize the matrices\n");
    //init_matrix<double>(A, m, k);
    init_matrix<double>(B, k,n);
    printf("Initialize the results matrix to 0s\n");
    init_matrix<double>(C, m,n,0);
    
    printf("\ncompute the execution time\n");
    auto mkl_t1 = get_time();
    cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, m, n, k, alpha, A, k, B, n, beta, C, n);
    auto mkl_t2 = get_time();

    printf("Execution time\n");
    auto mkl_time_span = duration_cast<duration<double>>(mkl_t2 - mkl_t1);
    cout << "Elapsed time MKL: " << mkl_time_span.count() << " s" << endl;

    //mkl_free(A);
    //mkl_free(B);
    //mkl_free(C);

    return 0;
    system("pause");
}

Answer 1

You could refer to the file under the below path regarding CBLAS_DGEMM example and prints the output data. Intel\oneAPI\mkl\2023.0.0\examples\examples_core_c\c\blas\source\cblas_dgemmx.c In addition, you could refer to the below link for more details regarding the usage of the routine.

https://www.intel.com/content/www/us/en/develop/documentation/onemkl-developer-reference-c/top/blas-and-sparse-blas-routines/blas-routines/blas-level-3-routines/cblas-gemm.html