token concatenation, #include, and all that

[Mike Haertel]

This question pertains to the ANSI C preprocessor (pick your brand, as
long as it conforms to the pANS.  I use GNU's.)

Suppose I have a macro ARCH defined as follows:

	#define ARCH "vax"

I would like to be able to say something like:

	#include archhdr("limits.h")

and have it expand to something like:

	#include "vax/limits.h"

Is there any way to do this?  I know I could do (fake) something similar:

	#define ARCH vax
	#define str(x) #x
	#define xstr(x) str(x)
	#define archhdr(x) xstr(ARCH##/##x) /* formally undefined but it
					       works with gcc */
	#include archhdr(limits.h)

However, this doesn't work if someone has #defined vax to be something else
(like, say, 1, but who would do a silly thing like that? :-).
Mike Haertel <mike at stolaf.edu>
In Hell they run VMS.