[boost] Re: errors building boost on MSVC71 - directory_iterator missing"advance" and "decrement" ?

From: David Abrahams (dave_at_[hidden])
Date: 2003-12-17 12:59:11

Beman Dawes <bdawes_at_[hidden]> writes:

> At 06:23 AM 12/17/2003, Bronek Kozicki wrote:
>
>  >I have two errors while building boost on MSVC71 (toolset vc7.1).
>  >Apparently boost::filesystem::directory_iterator should have member
>  >functions "decrement" and "advance", but these functions do not exist,
>  >at least on my platform.
>
> It is more complicated than
> that. boost::filesystem::directory_iterator is an input iterator. It
> is specified like this:
>
>      class BOOST_FILESYSTEM_DECL directory_iterator
>        : public boost::iterator_facade<
>        directory_iterator,
>        path,
>        boost::single_pass_traversal_tag >
>
> Perhaps I've got that wrong, but it has worked since the new-style
> iterator_facade was introduced, and it still compiles fine and passes
> all tests when built as a static library. See today's regression
> tests.
>
> The problem arises only when it is built as a Windows DLL.
>
> I could use some help on this. I don't understand why building as a
> DLL causes boost::iterator_facade to instantiate differently. Is the
> BOOST_FILESYSTEM_DECL the problem, and if so, what is the fix?

IIUC Exporting a class template in a DLL instantiates all of its
non-template member functions, so yes, that's the problem.

There are a few possible fixes:

  1. stop exporting it; make everything inline (you can dispatch to
     exported implementation functions).

  2. provide dummy advance and decrement functions

I'm sure there are a few others, but those are the ones that are
obvious to me.  I prefer #1 because it prevents misuse from compiling.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com