How to use boost :: preprocessor to unpack a sequence?

Question

How to use boost :: preprocessor to unpack a sequence of pairs?

For example, I have a sequence as shown below (the comma between doesn't matter)

(int,x)(double,y)(float,z) or (int,x),(double,y),(float,z) or ((int)(x))((double)(y))((float)(z)) 

and want to convert to

 int,double,float 

and

 x,y,z 

Using macor like

 UNZIP(i, seq) 

where i is the index.

Answer 1

Unzipping (int, x, 10)(double, y, 20)(float, z, 30) , i.e. a sequence without commas between elements.

Live demo

 #include <boost/preprocessor/punctuation/comma_if.hpp> #include <boost/preprocessor/seq/for_each_i.hpp> #include <boost/preprocessor/seq/pop_front.hpp> #include <boost/preprocessor/seq/for_each.hpp> #include <boost/preprocessor/variadic/elem.hpp> #include <boost/preprocessor/cat.hpp> // Such technique is used at: // http://www.boost.org/doc/libs/1_56_0/boost/fusion/adapted/struct/define_struct.hpp #define AUXILIARY_0(...) ((__VA_ARGS__)) AUXILIARY_1 #define AUXILIARY_1(...) ((__VA_ARGS__)) AUXILIARY_0 #define AUXILIARY_0_END #define AUXILIARY_1_END #define REMOVE_PARENTHESES(...) __VA_ARGS__ #define COMMA_SEPARATED(r, data, i, elem) \ BOOST_PP_COMMA_IF(i) BOOST_PP_VARIADIC_ELEM(data, REMOVE_PARENTHESES elem) \ /**/ #define ZIPPED_TO_SEQ(zipped) \ BOOST_PP_SEQ_POP_FRONT(BOOST_PP_CAT(AUXILIARY_0(0)zipped,_END)) \ /**/ #define FOR_EACH_ZIPPED_I(macro, data, zipped) \ BOOST_PP_SEQ_FOR_EACH_I(macro, data, ZIPPED_TO_SEQ(zipped)) \ /**/ #define UNZIP(i, zipped) FOR_EACH_ZIPPED_I(COMMA_SEPARATED, i, zipped) /*******************************************************************/ // DEMO: #define zipped (int, x, 10)(double, y, 20)(float, z, 30) FIRST: UNZIP(0, zipped) SECOND: UNZIP(1, zipped) THIRD: UNZIP(2, zipped) 

Preprocessor Output:

 FIRST: int , double , float SECOND: x , y , z THIRD: 10 , 20 , 30 

Answer 2

Assuming you meant commas ( (int,x),(double,y),(float,z) ), Boost.PP works fine:

 #include <boost/preprocessor.hpp> //or smaller individual headers //SEQ_ENUM adds commas between each element of the sequence //the sequence is transformed from what passed into the ... //the invocation of UNZIP_MACRO is given the index to use in each element as data #define UNZIP(i, ...) \ BOOST_PP_SEQ_ENUM( \ BOOST_PP_SEQ_TRANSFORM( \ UNZIP_MACRO, \ i, \ BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__) \ ) \ ) //called with each element of the sequence #define UNZIP_MACRO(s, data, elem) \ BOOST_PP_TUPLE_ELEM(data, elem) #define ZIPPED_SEQUENCE (int,x),(double,y),(float,z) UNZIP(0, ZIPPED_SEQUENCE) //int, double, float UNZIP(1, ZIPPED_SEQUENCE) //x, y, z