Size_t existence
"Every other compiler I've seen, that wants to insure that an include file is
only included once, uses a simple system of #ifndef / #define / #endif instead
of resorting to an entirely non-portable pragma."
Saying that one is simpler than the other is a matter of taste. From the ANSI C
library writer's perspective portability isn't a concern, so using a
non-portable pragma is perfectly acceptable.
The really ugly thing about using a macro definition, IMO, is that it tends to
breed code like:
#ifndef __FOO__
#include "foo.h"
#endif
etc.
This kind of code is messy, and typically is only there to speed up the compile
(ie, it has no semantic effect on the source). This is again a matter of taste,
but I feel that the increase in source clarity is worth the extra compiler
baggage. Using #pragma one relieves you from keeping track of what the file
name happens to be, and reduces the work involved in changing a header file's
name.
"Thanks for the tip on #pragma once == #define _H_stdio if that's what you
meant."
This is only true in THINK C.
"So what happens if you put any code before #pragma once? Does it get examined
twice? Or does this pragma magically prevent that include from being examined
in any way?"
As TFM will tell you, #pragma once marks a file as "read-once". Such files are
never re-read or re-opened.
-phil