How to do the equivalent of memset(this, …) without clobbering the vtbl?

Question

I know that memset is frowned upon for class initialization. For example, something like the following:

class X { public: 
X() { memset( this,          


        

Answer 1

You can use pointer arithmetic to find the range of bytes you want to zero out:

class Thing {
public:
    Thing() {
        memset(&data1, 0, (char*)&lastdata - (char*)&data1 + sizeof(lastdata));
    }
private:
    int data1;
    int data2;
    int data3;
    // ...
    int lastdata;
};

(Edit: I originally used offsetof() for this, but a comment pointed out that this is only supposed to work on PODs, and then I realised that you can just use the member addresses directly.)