Re: [Boost-users] [preprocessor] error: macro "BOOST_PP_SEQ_ELEM_III"

Quoting Reimund Klemm :

Why does this example compile with an error?:

#include #include #include

#define SEQ (b)(o)(o)(s)(t) #define i 0

int main( int argc, char* argv[]){ BOOST_PP_IF(i,BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_SUBSEQ(SEQ, 0, i)),0); return 0; }

You need to delay the evaluation of the branches. E.g. #include #include #include #define SEQ (b)(o)(o)(s)(t) #define i 0 #define TRUE_BRANCH(SEQ)\ BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_SUBSEQ(SEQ,0,i))\ /**/ #define FALSE_BRANCH(SEQ) 0 int main( int argc, char* argv[]){ BOOST_PP_IF(i,TRUE_BRANCH,FALSE_BRANCH)(SEQ); return 0; } should work. Pete