Question

I would expect an error inside the copy constructor, but this compiles just fine with MSVC10.

class Test
{
public:
    Test()
    {
        p = new int(0);
    }

    Test(const Test& t)
    {
        delete t.p; // I would expect an error here
    }

    ~Test()
    {
        delete p;
    }

private:
    int* p;
};

Answer 1

The issue that you are running into here is that you are not changing p per se (thus pstays immutable as you’re not changing its value), but you’re changing what p points to and thus are working at one additional level of indirection. This is possible because deleteing the memory associated with a pointer doesn’t change the pointer itself.

In a strict sense the const-ness of the object is preserved, even though its logical constness has been violated as you pulled the rug from underneath whatever p was pointing to.

As JonH mentioned in the comment, if you were not able to delete the object pointed to by a pointer held in a const object, you would end up with memory leaks because you wouldn’t be able to clean up properly after the object.