The other day I was working with libpulse in a Qt project. Because I didn't like to deal with a C library from C++ code I copied wrapper code from a well-proven project. Suddenly the wildest compile errors occurred when I only tried to include a header from the new code. After hours of frustration towards me, C++, the compiler and everything involved I discovered that one of the headers I copied had the same include guard as one of the existing classes.