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C ++ preprocessor - combining arguments

Is there a way for the C ++ preprocessor to concatenate arguments with a joiner token?

I found out what I can do:

#include <boost/preprocessor/seq/cat.hpp>
#define arg1 foo
#define arg2 bar
#define arg3 baz
BOOST_PP_SEQ_CAT((arg1)(_)(arg2)(_)(arg3))

to receive foo_bar_baz

.

I have two questions:

  • Is there a way to do this without iterating over the explicit character joiner ( (_)

    ) and for a variable length argument list?

  • Do I need to pass arguments like this:

    (arg1)(arg2)(arg3)

    Is it possible to wrap it in another macro that will allow me to pass the argument normally, i.e.?:

    arg1, arg2, arg3
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2 answers 


#define BOOST_PP_VARIADICS
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/seq/fold_left.hpp>
#include <boost/preprocessor/variadic/to_seq.hpp>

#define OP(s, state, x) BOOST_PP_CAT(state, BOOST_PP_CAT(_, x))
#define COMPOSE(...) BOOST_PP_SEQ_FOLD_LEFT(OP, BOOST_PP_SEQ_HEAD(BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)), BOOST_PP_SEQ_TAIL(BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__))) 

#define arg1 foo
#define arg2 bar
#define arg3 baz

COMPOSE(arg1, arg2, arg3)


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What about:



#include <iostream>

#define COMPOSE(prefix,name) prefix##_##name


int main() {
    int COMPOSE(first,par);

    first_par = 1;

    return first_par;
}
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