2014-05-28 22:20 GMT+08:00 TONGARI J <tongari95@gmail.com>:

2014-05-28 21:53 GMT+08:00 Igor R <boost.lists@gmail.com>:

Hello,

 

I'm trying to make a macro for the following case (essentially, I have to translate a run-time decision to a compile-time one):

 

switch(i)

{

case 1: my_func(arg, offsetof(my_struct, arr[1].my_field))); break;

case 2: my_func(arg, offsetof(my_struct, arr[2].my_field))); break;

// etc. up to 10

}

 

If I could hard-code the whole function call into the macro, I could do something like this:

#define EXPR(unused, x, text) my_func(arg, offsetof(my_struct, arr[x].my_field))); break;

 

#define MY_MACRO(x) \
switch(x)\
{\
BOOST_PP_REPEAT(x, EXPR, _)\
}

 

However, I'd like to pass "arg" and "my_field" as parameters to this macro.

What would be the right way to do this?

Perhaps:

    #define EXPR(unused, x, data) \

    case x: my_func(BOOST_PP_TUPLE_ELEM(2, 0, data) , offsetof(my_struct, arr[x].BOOST_PP_TUPLE_ELEM(2, 1, data)))); break;

     

    #define MY_MACRO(x, arg, my_field) \

    switch(i)\

    {\

    BOOST_PP_REPEAT(x, EXPR, (arg, my_field))\

    }

Or if you don't insist on a PP solution, lambda may help as well:

 

    #define EXPR(unused, x, data) case x: f(x); break;

    #define MY_MACRO(x, arg, my_field) \

    auto f = [&](int i){ my_func(arg, offsetof(my_struct, arr[i].my_field))); } \

    switch(i)\

    {\

    BOOST_PP_REPEAT(x, EXPR, (arg, my_field))\

    }

(note: code not tested)

I guess your example is a contrived one, since you don't even need a switch...