Question

I have previously asked a question about matrix multiplication in OpenCV and managed to find the correct answer. However, when I try to do this, I get erroneous results:

#include <iostream>

#include <cmath>

#include "opencv2/core/core.hpp"

using namespace std;

int main() {

// Vars.
int a[4] = {3,2,1,4};
int b[4] = {2,5,6,1};

// Pointers
int *p1, *p2;
int res(5);

// Init.
p1 = &a[0];
p2 = &b[0];

for(int i=0;i<4;i++) {
    res += (*(p1+i) - 2)*(*(p2+i) - 3);
}
cout << res << endl; // This is fine!

unsigned int p[4] = {3,1,2,4};
cv::Mat testMat = cv::Mat(1,4,CV_8U,p);
cout << testMat << endl; // Shows [3, 0, 0, 0] !!!!!
cout << testMat.at<unsigned int>(0,3) << endl; // Displays 4


//cv::Mat resDot = testMat*(testMat.t());
cv::Mat testMatTransp(testMat.t());
cout << testMatTransp.at<unsigned int>(0,0) << endl; // Shows Jibrish 56928323
return(0);
}

Unless I am missing something, this could should print out all the information correctly, right? Am I supposed to call any destructor or anything? I thought it is based on RAII, so unless I use “new” based initialisation, I don’t need to call destructors. Is that right? Any nudge in the right direction would be appreciated!

Answer 1

in

cv::Mat testMat = cv::Mat(1,4,CV_8U,p);

CV_8U means 8 bit unsigned. If you change it to

cv::Mat testMat = cv::Mat(1,4,CV_32S,p);

it should work. Alternatively, changing

unsigned int p[4] = {3,1,2,4};

to

unsigned char p[4] = {3,1,2,4};

should work too