What (not) to do in a constructor

Fully usable object does not mean a fully initialized object, you may defer some initialization (think lazy) as long as the user does not have to think about it.

http://stackoverflow.com/questions/3905784/what-not-to-do-in-a-constructor

class Vector
{
public:
Vector(): mSize(0), mData(0) {}

// first call to access element should grab memory

private:
size_t mSize;
int mData[];
};