Why doesn't the C++ default destructor destroy my objects?

Question

The C++ specification says the default destructor deletes all non-static members. Nevertheless, I can\'t manage to achieve that.

I have this:

class N         


        

Answer 1

The default destructor looks like this:

~M()
{
}

The default destructor does not insert code to do anything with pointed-to things. What if you had n pointing to a stack variable? Automatically inserting a delete n would crash.

The default destructor calls the destructor on each member of the class (member.~T()). For a pointer, that's a no-op (does nothing), just like myint.~int() does nothing, but for member classes with defined destructors, the destructor is called.

Here's another example:

struct MyClass {
public:
    MyClass() { .. } // doesn't matter what this does

    int x;
    int* p;
    std::string s;
    std::vector v;
};

The default destructor in reality is doing this:

MyClass::~MyClass()
{
    // Call destructor on member variables in reverse order
    v.~std::vector(); // frees memory
    s.~std::string();      // frees memory
    p.~int*();             // does nothing, no custom destructor
    x.~int();              // does nothing, no custom destructor
}

Of course, if you define a destructor, the code in your destructor runs before the member variables are destroyed (obviously, otherwise they would not be valid!).