how to read matrix from text file to Mat in opencv

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This works for me for reading .txt files. Please include the relevant header files.

//To read data from a text file. 
//filename is the name of the text file
//rows and cols show dimensions of the matrix written in the text file

#include"stdafx.h"
#include<fstream>

using namespace std;
using namespace cv;

Mat ReadMatFromTxt(string filename, int rows,int cols)
{
    double m;
    Mat out = Mat::zeros(rows, cols, CV_64FC1);//Matrix to store values

    ifstream fileStream(filename);
    int cnt = 0;//index starts from 0
    while (fileStream >> m)
    {
        int temprow = cnt / cols;
        int tempcol = cnt % cols;
        out.at<double>(temprow, tempcol) = m;
        cnt++;
    }
    return out;
}

However, you must know the dimensions of the matrix beforehand. Any improvement is appreciated.

FileStorage fs("test.xml", FileStorage::WRITE);
Mat myMatrix = (Mat_<int>(3,3) << 1,2,3,4,5,6,7,8,9);
fs << "myMatrix" << myMatrix;
fs.release();

Mat myMatrix2;
FileStorage fs2("test.xml", FileStorage::READ);
fs2["myMatrix"] >> myMatrix2;
fs2.release();

Content of "test.xml":

 <?xml version="1.0"?>
 <opencv_storage>
 <myMatrix type_id="opencv-matrix">
   <rows>3</rows>
   <cols>3</cols>
   <dt>i</dt>
   <data>
     1 2 3 4 5 6 7 8 9</data></myMatrix>
 </opencv_storage>

http://docs.opencv.org/modules/core/doc/xml_yaml_persistence.html#