On Fri, Sep 14, 2012 at 9:10 AM, Georg-Johann Lay <avr@xxxxxxxx> wrote:
> Hi, consider the following C code that tries to compose literals that use
> gcc's P extension:
>
> #define VAL1(X, SUFFIX) \
> X##SUFFIX
>
> int x1 = VAL1 (0x123, P-2u);
>
> #define VAL2(X, SUFFIX) \
> X##P-2##SUFFIX
>
> int x2 = VAL2 (0x123, u);
>
> Compiling this runs into "error: exponent has no digits" error because
> cpp introduces a bad blank before the minus (same with +).
>
> cpp expands the code to (with -P -g3):
>
> #define VAL1(X,SUFFIX) X ##SUFFIX
> int x1 = 0x123P -2u;
> #define VAL2(X,SUFFIX) X ##P-2 ##SUFFIX
> int x2 = 0x123P -2u;
>
> Is this a bug or a feature?
Feature, try this:
#define VAL2_(X, SUFFIX) \
X##-##SUFFIX
#define VAL2(X, SUFFIX) \
VAL2_(X##P, 2##SUFFIX)
Bert
