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Ted · Guest

The stand libary that is a part of my compiler (BC++) has the typical
include guards in the header files, but it also wraps the #include of
the header in files that use it:

// _defs.h
//
#if !defined(___DEFS_H)
#define ___DEFS_H

// header stuff here

#endif /* ___DEFS_H */

// stdarg.h
//
#if !defined(___DEFS_H)
#include <_defs.h>
#endif

Is the guard in stdarg.h just to speed up compiles? It sure looks ugly
and is a lot of typing to adopt such technique.

Ted

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Trevor Morgan · Guest

Yes, the idea is that it speeds up compilation times. The point of
include guards is that the code in the header file only gets parsed
once for each compilation unit, but the preprocessor will still open
and inspect the file each time it encounters a #include.

With these extra 'external' include guards, each header file will only
be opened once.

This page contains a discussion as to whether it's actually worth it.:

http://www.gamearchitect.net/Articles/ExperimentsWithIncludes.html

Some compilers, such as Microsoft VCC, use a '#pragma once' mechanism
to achieve the same effect, with less typing.

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Guest

Ted wrote:

Ivan Vecerina · Guest

"Ted" <rt (AT) local (DOT) net> wrote in message
news:sD9Gf.18818$_S7.10797 (AT) newssvr14 (DOT) news.prodigy.com...
: The stand libary that is a part of my compiler (BC++) has the typical
: include guards in the header files, but it also wraps the #include of
: the header in files that use it:
:
: // _defs.h
: //
: #if !defined(___DEFS_H)
: #define ___DEFS_H
:
: // header stuff here
:
: #endif /* ___DEFS_H */
:
: // stdarg.h
: //
: #if !defined(___DEFS_H)
: #include <_defs.h>
: #endif
:
: Is the guard in stdarg.h just to speed up compiles? It sure looks ugly
: and is a lot of typing to adopt such technique.

Yes, this trick may help speed-up compiles on some platforms.

GCC, I believe, has an automated identification of include guards,
making the redundant check pointless (it is able to automatically
skip reading the included file's contents).

--
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