[boost] Question on DLL import/export

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-03-25 09:48:38

Reading http://www.boost.org/more/separate_compilation.html
I see suggestion that all library sources start with:

    #define BOOST_WHATEVER_SOURCE 
    #include <boost/whatever.hpp> 

Is there any particular reason why this define should be placed in source, and 
not in Jamfile for the library? E.g:

dll boost_program_options : ...some sources...
     : <define>BOOST_PROGRAM_OPTIONS_SOURCE
     .....
     ;

- Volodya