Preprocessor question

[Glenn Fowler[eww]]

In article <9433 at smoke.BRL.MIL>, gwyn at smoke.BRL.MIL (Doug Gwyn ) writes:
> In article <531 at ole.UUCP> ray at ole.UUCP (Ray Berry) writes:
> >#define VAL 3
> >#define STR(x) #x
> >  puts("val is " STR(VAL));
> >   Turbo C produces "3" for STR(VAL); Microsoft produces "VAL" and 
> >leaves it at that.  
> >   Which behavior is correct?
> 
> "Before being substituted, each argument's preprocessing tokens are
> completely macro replaced as if they formed the rest of the
> translation unit; no other preprocessing tokens are available."
> 
> So VAL is first expanded to 3 then the #3 is performed to produce
> "3".
unless things changed from the 86 draft, macro arguments subject to the
# and ## operators are not expanded before the # and ## operations, so
the above eventually produces:

	puts ( "val is VAL" ) ;

to get VAL expanded add one more macro level:

	#define STR(x)	#x
	#define XSTR(x)	STR(x)
	puts(STR(VAL) " is " XSTR(VAL));

to eventually get:

	puts ( "VAL is 3" ) ;
-- 
Glenn Fowler    (201)-582-2195    AT&T Bell Laboratories, Murray Hill, NJ
uucp: {att,decvax,ucbvax}!ulysses!gsf       internet: gsf at ulysses.att.com