I personally follow Boost’s recommendation. It’s perhaps one of the largest collection of C++ libraries of good quality around and they don’t have problem.
It goes like:
<project>_<path_part1>_..._<path_partN>_<file>_<extension>_INCLUDED
// include/pet/project/file.hpp
#ifndef PET_PROJECT_FILE_HPP_INCLUDED
which is:
- legal (note that beginning by
_[A-Z]
or containing__
is not) - easy to generate
- guaranteed to be unique (as a include guard) within a project (else you have two files at the same place)
- guaranteed not to be used for anything else (if you end another macro with
INCLUDED
you’re spoiling for a fight)
I’ve read about GUID but those look weird.
And obviously I’d rather than all compilers implement #pragma once
(or better, #pragma multiple
and “once” be the default behavior…)