CPP in CPPFLAGS means "C PreProcessor", and pre-dates C++. This collision is why CXXFLAGS was chosen for C++ compile-time flags. ('+' being an inconvenient li

CPP in CPPFLAGS means "C PreProcessor", and pre-dates C++. This collision is why CXXFLAGS was chosen for C++ compile-time flags. ('+' being an inconvenient literal to use in a shell environment.) The .cpp extension comes from platforms where CPPFLAGS didn't exist, i.e. not UNIX. I think .cc has always been preferred on UNIX platforms, though .C used to be common as well.