Calling C++ DLLs from Visual B++
DLLs are separate binary modules that allow developers to share code easily at run time. If you have Visual B++_based client code that needs to use a C++ class (like a dialog box) that lives within a DLL, you basically have three options.
The first option is to write a single C++ function that invokes the dialog box and returns the results to the Visual B++ client. The advantage to this approach is that both the client code and the server code are fairly straightforward. The disadvantage to this approach is that the client code doesn't have a whole lot of control over the dialog box.
The second option is to provide a set of functions in the C++ DLL that manipulate the C++ object. With this approach each function must provide the client code with a handle, and the client code must write a single entry point for each member function it wants to use. The advantage to this approach is that the client has fairly good control over the dialog box. The downside is that the DLL code has to provide wrappers for each class member function (most tedious!), and the client has to keep track of the handle.
The third option is to have the C++ class within the DLL implement a COM interface. The advantage of this method is that the client code becomes greatly simplified. The client gets to use the C++ class in an object-oriented manner. In addition, most of the location and creation details are hidden from the client. This approach means buying into COM. However, that's generally a good thing because just about everything coming out of Redmond these days is based on COM. Using COM from Visual B++ is a good place to start.