Re: [Boost-users] [preprocessor] Strange BOOST_PP_CAT behavior

From: John Femiani (JOHN.FEMIANI_at_[hidden])
Date: 2008-05-08 05:11:06

Sergey  wrote:
> 
> I can't understand problem with code like this:
> 
> #define SOME_SEQ (1)(2)(3)
> #define BAR_MACRO_1(S) BOOST_PP_SEQ_ENUM(BOOST_PP_SEQ_TAIL(S))
> #define FOO_MACRO(S) BOOST_PP_CAT(BAR_MACRO_, BOOST_PP_SEQ_HEAD(S) ##
(S))
                                              ^
                                                Are you missing a 1?

> 
> FOO_MACRO(SOME_SEQ)
> 
> After preprocessing it looks like
> BOOST_PP_CAT(BOOST_PP_SEQ_ENUM_, 
> BOOST_PP_CAT(BOOST_PP_SEQ_SIZE_, BOOST_PP_SEQ_SIZE_2)) (2)(3)
> 
> 
> If I replace BOOST_PP_CAT with my own macro:
> 
> #define MY_CAT(a, b) MY_CAT_I(a, b)
> #define MY_CAT_I(a, b) a ## b
> 
> Everything is all right after preprocessing:
> 2, 3
> 
> Why? What is wrong?
> 
> --
> Best Regards,
>  Sergey                          mailto:flex_ferrum_at_[hidden]