Code runner wont run on classes[Bug]

- VS Code Version: 1.54.3
- OS Version: Windows 10
- Code Runner Version: v0.11.3

When I run a class with the code runner, it will show error that the functions inside the class are undefined.

1) I created a class in header file and source file named matrix.hpp and matrix.cpp.
1.1) I created the class Matrix inside the namespace mat.
2) I created the constructor matrix(const int rows, const int cols, double val =0);
3) I created the print function that print out the created matrix object.

When I run the code I get this kind of error:
"undefined reference to 'mat::Matrix::Matrix(int, int, double)'"
"undefined reference to 'mat::Matrix::print()'"

**Expected behavior**
the function should print out matrix like this:
mat::matrix mat(3,4)
mat.print();
// prints out:
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0

**Screenshots**