Re: [Boost-users] gcc3.2 preprocessor concatenation or not onnegativenumbers

From: Andy Little (andy_at_[hidden])
Date: 2006-01-21 04:53:28

"Paul Mensonides" wrote

> You aren't attempting to concatenate 1e and -1; you're attempting to
> concatenate
> 1e and -.  I.e. token pasting is only operating on the two adjacent
> preprocessing tokens...
>
> <1e> ## <-> <1>
>
> The result of this *should* be
>
> <1e-> <1>
>
> ...because 1e- is a valid pp-number.  However, it should not be <le-1>.  To
> make
> that, you'd have to first paste on the <->, then paste on the other number:
>
> #define CAT(a, b) PRIMITIVE_CAT(a, b)
> #define PRIMITIVE_CAT(a, b) a ## b
>
> CAT(CAT(1e, -), 1)
>
> This works for me (as it should) on gcc3.4.4.  I can't speak for gcc3.2.

Thanks Paul. It works on gcc3.2, however I need to use CAT(Sign, Number)  (or
Just Sign ## Number)  in the Macro too and then I get a bunch of warnings
saying:

test.cpp:25:22: warning: pasting "-" and "60" does not give a valid
preprocessing token

etc.

regards
Andy Little