How do I write into YML format and read it with opencv and C++ ?

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I'm following an OpenCV book tutorial to write and read into File Storage. It's supposed to write a file named "test.yml", then store some value in it and read that file again. Here's the code from the book :

#include <iostream>
#include <string>
#include "opencv2/core.hpp"
using namespace cv;
using namespace std;

int main (int, char** argv){
        //create writer
        FileStorage fs("test.yml", FileStorage::WRITE);

        //save an int
        int fps = 5;
        fs << "FPS" << fps;

        //create some Mat sample
        Mat m1 = Mat::eye(2,3, CV_32F);
        Mat m2 = Mat::ones(3,2, CV_32F);
        Mat result = (m1+1).mul(m1+3);

        //write result
        fs << "Result" << result;

        //release file
        fs.release();

        //create reader
        FileStorage fs2("test.yml", FileStorage::READ);

        Mat r;
        fs2["Result"] >> r;
        cout << r << endl;
        fs2.release();
        return 0;

}

WHAT HAVE I TRIED :

There's no error when I run the program, but there's no output (blank) and no *.yml file generated. Therefore I don't know where to go from here. However, I've been trying several things :

1. According to OpenCV docs, adding "open" is necessary when reading, so I modified into this :

   int main (int, char** argv){
   
       //create writer
       FileStorage fs, fs2;
       fs("test.yml", FileStorage::WRITE);
   
       //...
   
       //create reader
       fs2.open("test.yml", FileStorage::READ);
   

   But still empty result.

2. Then I tried to check if there's actually any data in it. I added checking code :

   //create reader
   fs2.open("test.yml", FileStorage::READ);
   
   Mat r;
   fs2["Result"] >> r;
   
   if (!r.data)
   {
           //Fails
           cout << "Could not open file. " << endl;
           return -1;
   }
   cout << r << endl;
   fs2.release();
   return 0;
   

   It return "Could not open file". Turn out, there's no *.yml file generated in my active / project working directory. If this information is relevant, I compile using CMake in terminal Ubuntu.

3. Added cout to check if my matrices have the correct value and are actually there.

    cout << "FPS " << fps << endl;
   
    cout << "Matrix One :" <<"\n" << m1 << endl;
    cout << "Matrix Two :" <<"\n" << m2 << endl;
    cout << "Result :" <<"\n" << result << endl;
   

   The matrices were printed out correctly. But the .*yml file won't be generated.

4. I thought maybe my code has some bugs, so I tried to run example code from OpenCV Docs : XML/YAML Persistence, and I encountered the same thing. I can run the program, there's no error but no *.yml file generated. I've been dealing with this for 2 days, what did I miss here ?