Difference between CPPFLAGS and CXXFLAGS in GNU Make

CPPFLAGS is supposed to be for flags for the C PreProcessor; CXXFLAGS is for flags for the C++ compiler.

The default rules in make (on my machine, at any rate) pass CPPFLAGS to just about everything, CFLAGS is only passed when compiling and linking C, and CXXFLAGS is only passed when compiling and linking C++.

By default, CPPFLAGS will be given to the C preprocessor, while CXXFLAGS will be given to the C++ compiler.

The GNU Make Manual is a good resource for questions like this (see Implicit Variables).

CPPFLAGS are for the C preprocessor, while CXXFLAGS are for the C++ compiler.

See here.