rcd@opus.UUCP (05/09/84)
It has already been noted (see ref) that you can concatenate tokens with
the preprocessor (at least in 4.x BSD; I don't know whether this is
epidemic) with:
#define CAT(x,y) x/**/y
with the preprocessor discarding comments. As noted earlier, this is not
only grungy, it gives lint a lot of grief.
---
A second solution is to use the interpretation of \ at end of line:
#define CAT(x,y) x\
y
which seems a little cleaner, but I'm still dubious; it seems like a dark
corner. I think it's safe to conclude that the preprocessor can't rejoin
lines when the first ends with \, but that the lex. analyzer must do so...
Still, I don't like it very much.
---
Yet a third, and in some sense the one that seems least grungy (but it's
the fault of nbires!vjs if you don't like it:-) is:
#define I(x) x
#define CAT(x,y) I(x)y
I is just an "identity macro" which gives you a chance to get something
between the x and y (a parenthesis) in the definition of CAT.
---
Anyone care to comment on esthetics? I'd also like to hear of compilers
for which the latter two don't work.
--
...Nothing left to do but smile, smile, smile. Dick Dunn
{hao,ucbvax,allegra}!nbires!rcd (303) 444-5710 x3086