[Araq]

This is very true; however c2nim distinguishes between #def and #define for this reason and this helps a lot. #def means c2nim needs to expand the macro, #define means it's some macro that should be translated into a Nimrod template. Coming up with heuristics to do this #def vs #define distinction automatically seems to be quite easy and might be implemented in a later version of c2nim.

[WalterBright]

#def, according to https://github.com/Araq/Nimrod/blob/master/doc/c2nim.txt, requires modification of the C header files. I don't think this is a practical option, for example, they might be system .h files.