Why does “delete *this” ever compile?

Question

I am deriving a class from MFC CDialogEx:

class MyDialog : public CDialogEx
{
  public:
    virtual void PostNcDestroy();
    …
  …
};

I implemented PostNcDestroy as such:

void MyDialog::PostNcDestroy()
{
    CDialogEx::PostNcDestroy();
    delete *this; // oops, typo
}

I was surprised to see that this code compiles (using VC120, or Visual Studio 2013) , and generates no warning at all. Can anybody tell why this is the case?

Thank you.

Answer 1

It's an implicit conversion; the class CWnd has an operator HWND() conversion function, and HWND is a pointer type.

Deleting that HWND is an error, but the compiler doesn't know that and can't warn you.

Answer 2

Why does “delete *this” ever compile?

It's possible to write a simple mcve that reproduces the behaviour that you're asking about:

struct foo {
    operator int*() {
        return nullptr;
    }

    void bar() {
       delete *this; 
    }
};

int main() {
    foo f;
    f.bar();
}

This compiles because foo is implicitly convertible to a pointer type. Same could be the case for your class.