Question

I wrote the following code:

int _tmain(int argc, _TCHAR* argv[])
{

int vals[]={1,2,3,4,5,6,7,8,9};

CvMat mat = cvMat(3,3,CV_8UC1,vals);

for(int i=0;i<mat.rows;i++)
{
    int* ptr = (int*) (mat.data.ptr + i* mat.step);

    for(int j=0;j<mat.cols;j++)
    {
                printf("%d\t",*ptr++);

    }
    printf("\n");
}

return 0;
}

The output I got is:

1              2               3
512            768             1024
196608         262144          327680

The matrix is not initialized properly. The pointer ptr points to the beginning of each row and incrementing it gives the element in corresponding column. Is my assumption correct? Is there any mistake with the cvMat constructor used or the access method of elements?

Answer 1

Why dont you use the cv::Matclass?

It has some handy functions which handle memory better.

for declaring and initializing cv::Mat in your case the code will look like this:

int main()
{
   int vals[] = {1,2,3,4,5,6,7,8,9};

    Mat mat = cv::Mat(3, 3, CV_8UC1, vals).clone();

    for(int i = 0; i < mat.rows; i++)
    {
        for(int j = 0; j < mat.cols; j++)
        {
             cout << mat.at<uchar>(j,i) << " ";
        }
        cout << endl;
    }
    return 0;
}