#include header guard format?

Question

I know it makes little difference to a project but, assuming you use #defined header guards for your C++ code, what format do you use? e.g. assuming a header called foo.hpp:

#ifndef __FOO_HPP__
...

#ifndef INCLUDED_FOO_HPP
...

#ifndef SOME_OTHER_FORMAT

I'm sold on the idea of upper-case #defines but cannot settle on a format for these guards.

Answer 1

I always use use

#ifndef FOOBAR_CPP

Answer 2

I always use INCLUDED_FOO_HPP

I wouldn't use the double underscore one, because starting things with double underscores is reserved.

Answer 3

I tend to use:

#ifndef FILE_DATE_H_

(replace _H_ with the appropriate extension like _HPP_, etc). The date stamp is to avoid collisions with other same named headers in other directions/libraries.

so in the end it looks like this:

#ifndef SOMEFILE_20082411_H_

Answer 4

Personally, i just use the filename FOO_HPP. Google uses the whole path like SRC_ENGINE_FAST_HPP.

Certain sets of names and function signatures are always reserved to the implementation:

• Each name that contains a double underscore (_ _) or begins with an underscore followed by an uppercase letter (2.11) is reserved to the implementation for any use.
• Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.

(17.4.3.1.2/1)

Answer 5

If you are using Visual Studio or a Microsoft compiler use the pragma way

#pragma once

Answer 6

I use

<FILENAME_IN_ALL_CAPS>_<YYYYMMDD>

or

<FILENAME_IN_ALL_CAPS>_INCLUDED_<YYYYMMDD>

Keeping it synchronous with folder hierarchies is too annoying (friend of refactoring), GUIDs are too annoying, the date suffix is good enough. If I would have to equally named files on the same day, I would

<FILENAME_IN_ALL_CAPS>_<YYYYMMDD>a
<FILENAME_IN_ALL_CAPS>_<YYYYMMDD>b
<FILENAME_IN_ALL_CAPS>_<YYYYMMDD>...