Memory leak in the implementation of the matrix multiplication operation - c++

Question

Memory leak in the implementation of the matrix multiplication operation:
template <typename T>
class Matrix
{
private:
T *data = nullptr;
size_t rows;
size_t cols;
Here is the multiplication operation itself:
Matrix<T> operator*(const Matrix<T> &other)
{
Matrix<T> result(rows, other.cols);
if (cols == other.rows)
{
for (size_t i = 0; i < rows; i++)
{
for (size_t j = 0; j < other.cols; j++)
{
for (size_t k = 0; k < cols; k++)
{
result.data[i * other.cols + j] += data[i * cols + k] * other.data[k * other.cols + j];
}
}
}
}
else
{
throw std::logic_error("Matrix sizes do not match");
}
return result;
}
How can I change this method so that it works correctly (and does not fall on tests)?
Here is a link to the class https://godbolt.org/z/4PPYx4Y3j. For some reason, everything works well here, but when I start doing a test:
TEST(testMatrixCalculations, testMultiplication)
{
myMatrix::Matrix<int> mat1(3, 3);
myMatrix::Matrix<int> mat2(3, 3);
for (auto &it: mat1)
{
it = 3;
}
for (auto &it : mat2)
{
it = 3;
}
mat1.printMatrix();
mat2.printMatrix();
myMatrix::Matrix<int> mat3 = mat1 * mat2;
mat3.printMatrix();
for (auto it : mat3)
{
ASSERT_EQ(it, 27);
}
}
Outputs this:
3 3 3 3 3 3 3 3 3
3 3 3 3 3 3 3 3 3
-1119477653 32718 -1119477653 32718 775685387 21966 775685387 21966 27
Failure
Expected equality of these values:
it
Which is: -1119477653
27

Answer 1

Your result.data is not initialized to 0 but you apply a += operation to it. You must either initialize your Matrix::data member to zero in the Matrix main constructor function, or initialize it preliminary in your multiplication loop.
for (size_t i = 0; i < rows; i++) {
for (size_t j = 0; j < other.cols; j++) {
result.data[i * other.cols + j] = 0;
for (size_t k = 0; k < cols; k++) {
result.data[i * other.cols + j] += data[i * cols + k] * other.data[k * other.cols + j];
}
}
}