Question

I have a matrix class and, with the following constructor:

template<class T>
Matrix<T>::Matrix(unsigned rows, unsigned cols) :
        rows(rows), cols(cols) {
    index = 0;
    data_ = new T[rows * cols];
}

template<class T>
Matrix<T>::~Matrix() {
    delete[] data_;
}

When I’m calculating the inverse of the matrix, I would like to free the memory of the
temporary variable called a:

template<class T>
Matrix<T> Matrix<T>::inverse() {
    unsigned i, j, k;
    Matrix<T> a(2 * rows, 2 * rows);        
    ....
    return tmp;
}

I thought that this variable would be destroyed in the end of the function, but when I test:

for (int i = 0; i < 3; i++) {   
        Matrix<double> m(5, 5);
        m << 5, 2, 4, 5, 6, 1, 3, 1, 2, 5, 2, 5, 2, 7, 2, 9, 2, 1, 0.1, 0.43, 1, 0, 0, 0, 1;
        m.inverse();
        std::cout << m << std::endl;
    }

In the first loop the a is initialized with zeros, but the next step the initial values of the a is the previous values, so a(k+1)=a_endvalues(k). Why is it like this?

Answer 1

The problem is that you are not initializing the elements of your dynamically allocated array in the constructor. To ensure that the array has default constructed or zero-initialized elements, you need to do this in your constructor:

template<class T>
Matrix<T>::Matrix(unsigned rows, unsigned cols) :
        rows(rows), cols(cols) {
    index = 0;
    data_ = new T[rows * cols]();
                //             ^ HERE!
}

But as has been pointed out in comments, you could make your life easier by using an std::vector<T>:

template<class T>
Matrix<T>::Matrix(unsigned rows, unsigned cols) :
        rows(rows), cols(cols), data_(rows*cols) 
{ }