How does multiple implementing multiple COM interfaces work in C++?
- by Martin
I am trying to understand this example code regarding Browser Helper Objects.
Inside, the author implements a single class which exposes multiple interfaces (IObjectWithSite, IDispatch).
His QueryInterface function performs the following:
if(riid == IID_IUnknown) *ppv = static_cast<BHO*>(this);
else if(riid == IID_IObjectWithSite) *ppv = static_cast<IObjectWithSite*>(this);
else if (riid == IID_IDispatch) *ppv = static_cast<IDispatch*>(this);
I have learned that from a C perspective, interface pointers are just pointers to VTables. So I take it to mean that C++ is capable of returning the VTable of any implemented interface using static_cast.
Does this mean that a class constructed in this way has a bunch of VTables in memory (IObjectWithSite, IDispatch, etc)? What does C++ do with the name collisions on the different interfaces (they each have a QueryInterface, AddRef and Release function), can I implement different methods for each of these?
