Boost preprocessor library

[AdrianH]

I'm having some trouble expanding to the base value

 # include <boost/preprocessor/cat.hpp>

 #define REL_ITERATION_1 1
 #define REL_FRAME_ITERATION(i) BOOST_PP_CAT(REL_ITERATION_, i)
 #define REL_ITERATION_PARAMS_2 REL_FRAME_ITERATION(1)
 #define REL_FRAME1(i)           BOOST_PP_CAT(REL_ITERATION_PARAMS_, i)
 #define REL_FRAME2(i)           REL_ITERATION_PARAMS_##i
 REL_FRAME1(2)
 REL_FRAME2(2)

Here's the output.

BOOST_PP_CAT(REL_ITERATION_, 1)
1

Does anyone have any idea why the first call is not the same as the second? I thought I had a handle on using the preprocessor, but I just don't get this. :(

[AdrianH]

Never mind. I missed the part in the documentation where it says if it expands to a BOOST_PP_CAT() macro, it won't expand it.

Doh!