How to load COM DLL at runtime

Question

I have a VB6 COM DLL. I want to use it from C++. I know how to register it, generate a tlb file from the DLL, and #import it in C++.

I'd like however, to load and use DLLs like this dynamically, at runtime, without knowing them in advance. Is this possible?

Thanks,

Answer 1

Yes, but you need to get the question clearer.

Sometimes, you do know the COM interface upfront, just not the implementation. In that case, you can create a dummy implementation of the interface and #import that. At runtime, you'd still register the real component, get an object from it (via CoCreateInstance probably) and store that in an appropriate smart pointer.

With VB6, it's a bit less direct. This adds a level of indirection. Read up on IDispatch. You need to get that known interface to describe an unknown interface. That way, the unknown interface can be obtained at runtime.

Answer 2

IMHO, You need at least some common interface (so you known what to call in the C++ side).

I'd do something like:

1. Define a common interface (in its own DLL/TLB)

2. Implement this interface in one or more COM servers

3. Import this interface in the C++ side (let's call it client)

4. Define a way to pass the progid of the COM server you want to work with (load dynamically) in the client.

Hope this helps

Answer 3

Take a look at these two MSDN articles about Registration-Free Activation of COM Components:

• Registration-Free Activation of COM Components: A Walkthrough
• Escape DLL Hell: Simplify App Deployment with ClickOnce and Registration-Free COM

There also have been some similar question here on StackOverflow:

• Generate manifest files for registration-free COM
• Windows/C++: how to use a COM dll which is not registered