If your header files are huge, #pragma once is a lot faster than the #ifndef approach.

That''s because if your header file is 500K large (just look at the Win32 headers), everytime the file is included, the compiler will need to read 500K from the #ifndef just to find the #endif. This IS a major waste of time, especially if the file is included many times.

While #pragma once isn''t standard, it is supported by many compilers, MSVC, lcc-win32, gcc, probably others that I haven''t tried. My opinion? Use it

Well, if your header files are huge and you''re desperate, you could always create a small header file like:

#ifndef _THISXYZ_INCLUDED_
#define _THISXYZ_INCLUDED_

#include "my_huge_header_file.h"

#endif

That way you''d at least be rid of the scanning through the huge file more than once.

I think it should also be mentioned that you don''t need to do such things as:

#ifdef _MSVC
#pragma once
#endif

Just leave it as this:

#pragma once
#ifndef __THISFILE_H__
#define __THISFILE_H__

...

#endif

The #pragma won''t choke a compiler that doesn''t support it. Thats one of the things about #pragmas. They''re there to use specific features, yet if the compiler doesn''t understand, then it just ignores it (some compiler will give a warning that it didn''t understand it, but code will still compile).


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I guess this is where most people put a famous quote...
"Everything is funnier with monkey''''s" - Unknown

Ah, goody goody.

-SirKnight

quote:

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Original post by Promiscuous Robot

The #pragma won''t choke a compiler that doesn''t support it. Thats one of the things about #pragmas. They''re there to use specific features, yet if the compiler doesn''t understand, then it just ignores it (some compiler will give a warning that it didn''t understand it, but code will still compile).

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But what if 2 compilers interpret the same directive in different ways?

Then you''re boned
You need those #ifdef _SOLARIS type things (commonly used one to fix sun''s broken realloc...)

Are not ALL #pragma''s, by definition, compiler dependent?

Magmai Kai Holmlor
- The disgruntled & disillusioned