Difference between VS 2015 and cpp.sh

[etrusks]

Hi, lets ignore the fact that this is very bad matrix class. The elements are being allocated in the line no matter what the dimensions are. I just tried to create operator[]() for fun and optional member function default_init() that initializes every element to default. So it can be used if elements actually have default value.

On visual studio this code dont really work because when I cout << elements in main() they have all kinds of random values.

If I run this on cpp.sh that every element is correctly initialized to its default value 0.

Why exactly this is happening? Problem in code?

#include <iostream>

using namespace std;

template<class T>
class Matrix {
	int dim1;
	int dim2;
	int sz;
	T* elem;
public:
	Matrix(int d1, int d2) : dim1{ d1 }, dim2{ d2 },
		sz{ dim1 * dim2 }, elem{ new T[sz] } {}
	~Matrix() { delete[] elem; }


	int size() { return sz; }
	void default_init();
	T& operator[](int);
};

template<class T>
void Matrix<T>::default_init(){
	T* p = elem;
	for (int i = 0; i < sz; ++i) {
		*p = T{};
	}
}

template<class T>
T& Matrix<T>::operator[](int index) {

	return *(elem + index);
}

int main() {

	Matrix<int> m{ 1,6 };
	m.default_init();

	std::cout << m[0] << std::endl;
	std::cout << m[1] << std::endl;
	std::cout << m[3] << std::endl;
	std::cout << m[4] << std::endl;
	std::cout << m[5] << std::endl;

}

Output VS 2015

0
-842150451
-842150451
-842150451
-842150451
-842150451

Output cpp.sh

0
0
0
0
0
0

[Peter87]

You initialize p to point at the first element in the array. p is never changed so only the first element is set to zero.

[etrusks]

ohh man I'm so ashamed of myself. Thank you man! Don't have idea why it worked on cpp.sh
I'm sry for posting this. :(

[Moschops]

It didn't work on cpp.sh ; on cpp.sh, you only set the first to zero. The other values could be anything at all. On cpp.sh, it seems that they happen to be zero.

[etrusks]

Ohh yea just checked it out with other number instead of default. Thanks man!