Visual Basic and C++ and Debug and DLLs

Here is the problem I am having now. I have a C++ DLL that seems to work just fine. It has been tested with function calls from a executable written in C++. Now, using it with my Visual Basic GUI seems to be ok up to a point. The Visual Basic program compiles and "links" (for lack of a better term to use) with the DLL written in C++. But it seems that I cannot pass the same sort of variables back and forth between the Visual Basic program and the DLL. It seems to crash on the DLL side after a function call is made.

So my question is this. How can I run the two -- the Visual Basic GUI and the C++ DLL -- in debug mode so that I can watch what is happening on the DLL side?

And/Or, if I put a printf statement in the DLL C++ code, where would the output go to?

as far as I know, it's not possible - only in .NET it's possible, and that's considered
new idea.
you probably get errors because of type mismatch: for example VB type of Integer
might not be identical "behind the scenes" to the "int" of C language.
I'm not familiar enough with those things to help much further, but at least you have
something to explore.

also, to "debug" the dll you can add code in there that writes into
text file. call the file "debug.txt" and check it after you execute
the application.