Question of using CV::MatConstIterator

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I am new learner for opencv,so i wan to ask some question about it. I type some codes, which can find in the book learning opencv3 ,but error has occur when i use the CV::MatConstlerator. The error is that it is not contain a list of template parameters .It make me confused. Pleace help to understand.Thank you very much.

codes are as followed:

#include"iostream"
#include"opencv2/core/core.hpp"
#include"opencv2/highgui/highgui.hpp"

using namespace std;
using namespace cv;
int main()
{

    int sz[3] = { 4,4,4 };
    Mat m(3, sz, CV_32FC3);
    randu(m, -1.0f, 1.0f);

    float mat = 0.0f;
    MatConstIterator<Vec3f>it = m.begin();



    system("pause");
}