Re: [Boost-users] Preprocessor thingy

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-06-17 17:00:05

Johan 't Hart wrote:
> Hi,
> 
> I don't know if boost has a solution for my problem, or there is just
> something simple I miss...
> I've been struggling with some preprocessor things. I'm trying to use it for
> versioning. Here is the problem:
> 
> I've got these defines:
> 
> #define VERSION_MAJOR 5
> #define VERSION_MINOR 4
> #define VERSION_BUILD 3
> #define VERSION_SUBBUILD 2
> 
> Sometimes I just need a string like: "5.4.3.2". I do it like this:
> 
> #define STRINGER_(s) #s
> #define STRINGER(s) STRINGER_(s)
> #define VERSION_STRING_1        \
>     STRINGER(VERSION_MAJOR) "." \
>     STRINGER(VERSION_MINOR) "." \
>     STRINGER(VERSION_BUILD) "." \
>     STRINGER(VERSION_SUBBUILD)
> 
> So VERSION_STRING_1 is "5.4.3.2"
> Now I need a string like: "5.4.3b". (Note the 'b'. When VERSION_SUBBUILD ==
> 3, I want it to be a 'c' etc)
> How do I do this in a preprocessor command???? The char is simple, its
> (VERSION_SUBBUILD+'a'-1). 

You need a lookup table to do it all in the preprocessor, AFAIK:

     #include <boost/preprocessor/cat.hpp>
     #include <boost/preprocessor/stringize.hpp>

     #define VERSION_ID(major,minor,build,sub_build) \
         BOOST_PP_STRINGIZE( \
             major.minor.build.BOOST_PP_CAT(N2LCC_,sub_build) )

     #define N2LCC_1 a
     #define N2LCC_2 b
     #define N2LCC_3 c
     #define N2LCC_4 d
     #define N2LCC_5 e
     #define N2LCC_6 f
     #define N2LCC_7 g
     #define N2LCC_8 h
     #define N2LCC_9 i
     #define N2LCC_10 j
     #define N2LCC_11 k
     #define N2LCC_12 l
     #define N2LCC_13 m
     #define N2LCC_14 n
     #define N2LCC_15 o
     #define N2LCC_16 p
     #define N2LCC_17 q
     #define N2LCC_18 r
     #define N2LCC_19 s
     #define N2LCC_20 t
     #define N2LCC_21 u
     #define N2LCC_22 v
     #define N2LCC_23 w
     #define N2LCC_24 x
     #define N2LCC_25 y
     #define N2LCC_26 z

     VERSION_ID(2,1,3,1)

Regards,
Tobias