On 8 March 2010 03:21, Vladimir Prus <vladimir@codesourcery.com> wrote:
Paul wrote:

> Hi all,
>
> I'm confused about boost dynamic linking on windows MSVC90
>
> I always define: BOOST_ALL_NO_LIB
> So that I directly control which DLLs I link to.
> I add the signals dll for linking.
>
> Then, if I define BOOST_ALL_DYN_LINK, I get lots of these messages:
>
> boost_1_42_0\boost/signals/detail/signal_base.hpp(113) : warning C4251:
> 'boost::signals::detail::signal_base_impl::combiner_' : class 'boost::any'
> needs to have dll-interface to be used by clients of class
> 'boost::signals::detail::signal_base_impl'
> 39>        boost_1_42_0\boost/any.hpp(36) : see declaration of 'boost::any'
>
> I've read up on this and understand why the warnings are shown.
>
> BUT,
> I don't understand why I am able to still link my program if I do NOT define
> BOOST_ALL_DYN_LINK.
>
> Without the flag, it compiles without warnings, it links without problems,
> AND the executable requires the signals DLL to be available, so clearly it
> IS dynamically linked.  Right?

Do you include import library for Boost.Signals in the link? Then, presumably,
compiler automatically 'dllimports' the symbol. Please see:

       http://blogs.msdn.com/oldnewthing/archive/2006/07/26/679044.aspx

Does this help?

- Volodya


This DOES help a lot !

So, I have a few options:

1) Define BOOST_ALL_DYN_LINK and put up with the excess warnings.
   This would be ok if the boost developers could "fix" their headers by adding #pragmas to hide the warnings when they know its not a problem.

2) Define BOOST_ALL_DYN_LINK and write a couple of header files that wrap the boost headers with #pragmas (eg especially for boost::signals)

3) Do not define BOOST_ALL_DYN_LINK, and allow Windows the link "the naive way", which might give slower performance, but maybe not.

Thanks Volodya !