Weird segmentation fault 11 - c++

Question

There are two files:
Matrix.hpp:
template <typename T>
class Matrix {
private:
size_t rows = 0;
size_t cols = 0;
T* data = nullptr;
public:
Matrix() = default;
~Matrix();
Matrix(size_t n, size_t m);
T& operator() (size_t i, size_t j);
};
template <typename T>
Matrix<T>::Matrix(size_t n, size_t m) : rows(n), cols(m) {
try {
data = new T[rows*cols];
} catch (const std::bad_alloc& e) {
std::exit(EXIT_FAILURE);
}
};
template <typename T>
Matrix<T>::~Matrix() {
delete[] data;
}
template <typename T>
T& Matrix<T>::operator()(size_t i, size_t j) {
if (i < rows && i >= 0 && j < cols && j >= 0) {
return data[(i+1)*cols + (j+1)];
} else {
throw std::logic_error("matrix indices out of range");
}
}
and
Main.cpp:
#include <iostream>
#include "Matrix.hpp"
int main() {
size_t n, k;
std::cin >> n >> k;
Matrix<long double> m = {n, k};
for (size_t i = 0; i < m.getNumRows(); ++i) {
for (size_t j = 0; j < m.getNumCols(); ++j) {
std::cin >> m(i,j);
}
}
for (size_t i = 0; i < m.getNumRows(); ++i) {
std::cout << "\n";
for (size_t j = 0; j < m.getNumCols(); ++j) {
std::cout << m(i, j) << " ";
}
}
return 0;
}
When I'm entering something like:
1 2 3 4
I can get
3 4
as answer but sometimes the same input causes Segmentation fault 11 moreover when I'm changing template argument from long double to int, error disappears. How can I fix it?

Answer 1

Your operator function is accessing data outside its bounds.
Passing (0,0) to the function should return data[0]. Currently it returns data[2].
Change line
return data[(i+1)*cols+(j+1)];
to
return data[i*cols+j];