Thread: General Guidelines on Preventing Header File collision

Are you talking about inclusion guards? (Search for that and you'll probably find a lot of information).

Basically, you use

Code:

#ifndef SOMETHING
#define SOMETHING

/* contents of header file . . . . */

#endif

That prevents a header file from being included more than once.

[edit] There was a thread about this earlier today: http://cboard.cprogramming.com/showthread.php?t=104721 [/edit]

I guess a good rule of thumb would be to include the most general header first. Including a specific header file first would likely draw in the generic header files, so putting the generic header files after specific ones would just be useless.

Might be a coincidence, but I think that windows.h is more generic than winnt.h or wchar.h . . . .

Oh well, what do I know.

Anyway, there's no real way to tell which header should be included before other headers. It depends on how they're created, and you can create header files however you like.

For headers, inclusion guards solve everything. I usually use the filename, replacing . with _. For example, fileio.h would be:

Code:

#ifndef FILEIO_H
#define FILEIO_H

// Stuff
#endif

If a.h requires that b.h be included before it, then a.h includes b.h itself. At the .cpp level, I can then #include in any order. (Except in some really exotic situations that were a result of me not thinking far enough into the future. Plan, plan, plan.) Now, if it's someone else's headers, then that's another story. I generally do:

Code:

// Standard C/C++ headers
// Headers for libraries, ie, SDL, curl, etc.
// Headers for this project.

Originally Posted by Drogin

When it comes to windows, he's like a...god

By that, I take it you mean many cite signs of his greatness but many others wonder if he actually exists.

Seriously, the general guideline is that header files should provide everything needed for them to be used: if there is no way for code to effectively make use of header A without also #include'ing header B (eg if header A makes use of definitions or declarations in header B) then header A should generally #include header B.

As an almost general rule, all headers should have #include guards as well. This is virtually mandatory if there is any chance of a header file being #include'd more than once (eg nothing prevents code from #including a header twice, and it is possible for some code to #include two headers that each include some other header). There are exceptions to this rule (eg a header file that works differently based on optional #define's which can be redefined between two inclusions), but anyone running into such exceptions will know exactly what they are doing.

The unfortunate thing is that some header files with some commercially available libraries fail to comply with such guidelines ..... so it is necessary for users of those libraries to work around such cases.