RE: [boost] BOOST_PP_REPEAT with internal macro problem

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2004-07-14 23:00:22

> -----Original Message-----
> [mailto:boost-bounces_at_[hidden]] On Behalf Of 

> BOOST_PP_REPEAT works great for me when used like:
> 
> #define MAX  5
> #define  CODE    my_code_goes_here
> BOOST_PP_REPEAT(MAX, CODE,  )
                            ^^
Passing nothing as a macro argument is undefined in C++.  You should use a
dummie argument instead--preferably not an identifier.  I usually use ~ or ?.

> 
> But it gets confused when used like:
> 
> #define MAX  (4+1)

Arkadiy is correct.  The library cannot understand the expression (4+1).  It can
only understand unadorned integer literals (such as 1, 2, 3, etc.) from 0 to
256.  If you need to do arithmetic, you have to use the arithmetic primitives of
the library, such as BOOST_PP_ADD or, in this case, BOOST_PP_INC (which is more
efficient).

Thus, if you want to do a repetition of MAX + 1, you need to say:

BOOST_PP_REPEAT(BOOST_PP_INC(MAX), CODE, ~)

Regards,
Paul Mensonides