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

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2006-01-20 16:52:34

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Andy Little

> Using gcc3.2  the concatenation of  1##Num  where Num is 
> negative leaves a space eg 1e#-1  --> 1e -1 as can be seen by 

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.

Regards,
Paul Mensonides