Hi,
I guess, this question is also related to the other thread: Need to render the camera view on a separate preview window in c++.
So I assume here, that the basic mechanism of showing a rendered image in a window is already clear (or will be explained by Riccardo).
So the question here is, how to render a specific or multiple cameras.
The normal procedure to render a scene in parallel to the user working is to clone the scene (C4DAtom::GetClone()) before passing the clone to RenderDocument(). And in the cloned document, you are free to change the active camera the way you need to.
A completely different approach (but with the drawback of getting the result only in Picture Viewer or as files saved to disk) may be to use the Takes system. You can set up multiple takes, assign a different camera each and afterwards use one of the "Render All Takes" or "Render Selected Takes" commands.
Last thing: Please consider to add tags to your threads, as I did for this one.
Cheers,
Andreas