> /usr/include/g++-v3/backward/iostream.h:35: using directive `ostream' > introduced ambiguous type `ostream'' > I know it's probably due to libraries versions mismatch, but I got libstdc++ > exactly the same version as gcc. I'm now pretty sure tha it is *not* due to library version mismatch, but due to a plain error in the code you are trying to compile. Do not declare a class 'ostream' yourself. Regards, Martin