Problem with const array changing c++

Question

Hi, I have this code that tries to protect the user from array boundary errors.

I don't get why this will compile, tho i've declared the array to be const, therefore, i'm suppose to get a compilation error!

thanks a lot.

/************ file: SafeAccessArray.h ********************/
template<typename T>
class SafeAccessArray
{
private:
int _len;
T * _arr;
public:
SafeAccessArray (int len=2) : _len (len), _arr (new T [len]) {}
~SafeAccessArray () { delete _arr; }
T& operator [](int i) const
{if (i < 0 || i >= _len) throw (-1);
else return _arr[i]; }
};
/************ end of file: SafeAccessArray.h *************/

/************ file: SafeAccessArray1.cpp *************/
#include "SafeAccessArray.h"
int main()`enter code here`
{
SafeAccessArray<int> intArr (2);
intArr[0] = 0;
intArr[1] = 1;
const SafeAccessArray<int> intArrConst (2); // THIS IS THE "PROBLEMATIC" LINE
intArrConst [0] = 0;
intArrConst [1] = 1;
return 0;
}
/************ end of file: SafeAccessArray1.cpp ******/

Answer 1

Yea it's const, but you did T& operator [](int i) const anyway. You're returning a reference, and this function can be called on a const object.

Make it return const T&. Better yet, stop. Just use std::vector and the at() function.

Answer 2

I think that operator[] member function desires the following two overloaded variants:

T& operator [](int i);
const T& operator [](int i) const;

The one provided

T& operator [](int i) const;

does not match any of the above, and hence the problem.