find one copy will result in inconsistencies within a program. In C, the usual convention is to give header files names that end with `.h'. It is most portable to use only letters, digits, dashes, and ...

"Include what you use" means this: for every symbol (type, function, variable, or macro) that you use in foo.cc (or foo.cpp), either foo.cc or foo.h should include a .h file that exports the ...