How to fill Matrix with zeros in OpenCV?

Question

The code below causes an exception. Why?

#include 
#include 

using namespace cv;
using namespace std;

void mai         


        

Answer 1

Mat img;

img=Mat::zeros(size of image,CV_8UC3);

if you want it to be of an image img1

img=Mat::zeros(img1.size,CV_8UC3);

Answer 2

Because the last parameter is optional and also the data pointer should point somewhere appropriate:

//inline Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step)
double mydata[1];
Mat m1 = Mat(1,1, CV_64F, mydata); 
m1.at<double>(0,0) = 0;

But better do it directly with this template-based constructor:

//inline Mat::Mat(int _rows, int _cols, int _type, const Scalar& _s)
Mat m1 = Mat(1,1, CV_64F, cvScalar(0.));

//or even
Mat m1 = Mat(1,1, CV_64F, double(0));