Naming Include Guards

Question

How are C++ include guards typically named? I tend to see this a lot:

#ifndef FOO_H
#define FOO_H

// ...

#endif

However, I don\'t think

Answer 1

As others mentioned before, a very common convention is to use the uppercase version of the name, and the dot replaced by an underscore: foo.h -> FOO_H

However, this can lead to name collisions with simple and/or common names. For this reason, autogenerated header like the stdafx.h in non-empty Visual C C++ projects append some random string, like:

#ifndef FOO_H__NsknZfLkajnTFBpHIhKS
#define FOO_H__NsknZfLkajnTFBpHIhKS
#endif

http://www.random.org/strings/ is a useful random generator for this.

Also, if the file is part of some submodule, or its contents reside in one specific namespace, I tend to add that to the guard too:

#ifndef SOMECOMPONENT_FOO_H__NsknZfLkajnTFBpHIhKS
#define SOMECOMPONENT_FOO_H__NsknZfLkajnTFBpHIhKS

namespace somecomponent
{
  ...
}

#endif