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In message <4as6dg$3ih@ets.cis.brown.edu> you write:
> I'm trying to figure out how to best include RCS version identifier
> strings into the various modules I'm compiling with gcc.  I've been
> running into two problems.
> 
> 1) With -Wall the compiler warns about the variable being unused
> 2) The compiler optimizes away the existence of the string

Hi James,
	I use the following piece of code:

------ RcsId.h ------
#ifdef __GNUC__
// Use Gnu's __attribute__ keyword to suppress warning.
#define ALT_RCSID(Id, Name) \
	static const char RCS_ID_##Name[] __attribute__((unused)) = Id
#else
// Grotty method of warning suppression
#define ALT_RCSID(Id, Name)				\
	static const char RCS_ID_##Name[] = Id;		\
	static void _DummyUseRCSIdFunction##Name(void)	\
	{						\
	  (void)_DummyUseRCSIdFunction##Name;		\
	  (void)RCS_ID_##Name;				\
	}
#endif /*GNU*/

#define DO_ALT_RCSID(x,y) ALT_RCSID(x,y)
#define RCSID(Id) DO_ALT_RCSID(Id, __LINE__)
------------------

We simply include "RcsId.h" then use 

RCSID("$Id");

At the *bottom* of the code.  This technique has the advantages that it
suppresses warnings, and also doesn't use the same identifier name for
every source file, allowing C++ templates to be used (where the C source
gets included).

The bad news is that you get a tiny extra function in each .o file.

Hope this at least gives you some ideas,
Rusty.
--
Rusty.Russell@adelaide.maptek.com.au           "Engineer? So you drive trains?"
Lies, damned lies, and out-of-date documentation.        #include <stddisclm.h>