13#error Need to compile with a C++ compiler, not a C compiler. The problem is that in Windows, filenames are case-insensitive. So the compiler cannot tell mumble.c from mumble.C. Visual Studio decided to make .cpp (which used to mean run the C preprocessor) mean C++ and both .c and .C mean C. The other problem is that when you insert a new file into a project, it FOR THAT FILE makes an override. The project settings say C++ but if you right-click on the file itself it has an override to compile with C. This needs to be changed for both the .C file and the .h file.