[boost] [exception] get_error_info with dynamic libraries

Subject: [boost] [exception] get_error_info with dynamic libraries
From: Pavel Lebedev (cygnus_at_[hidden])
Date: 2011-09-19 14:20:19

Hi, I believe there is a problem with boost::get_error_info
when used to retrieve error info objects added to exceptions in a module (exe/dll)
different from the one making the call to this function under MSVC++ 2010 SP1.

The problem appears to be introduced in SVN revision 68792 with a
fix for ticket #5178 that changed struct boost::exception_detail::type_info_
from storing a reference to type info to a pointer in member type_.
There's an assertion in function
boost::exception_detail::error_info_impl_container::get
that checks these members for equality which now does pointer comparison
instead of calling std::type_info::operator== (for the case of enabled RTTI).
This fails when used on error info added in the different module from the
one trying to access it because each module gets its own copy of std::type_info
object for the same type with different addresses, even though
std::type_info::operator= does string comparison of class names and would
have returned true, as it did before this change. Other compilers/platforms that
don't provide process-unique type info objects are most likely affected too.
The following patch appears to fix this problem for me by reverting to
compiler-provided way of comparing type info objects.

Index: info.hpp
===================================================================
--- info.hpp	(revision 74465)
+++ info.hpp	(working copy)
@@ -97,7 +97,7 @@
                     {
                     shared_ptr<error_info_base> const & p = i->second;
 #ifndef BOOST_NO_RTTI
-                    BOOST_ASSERT( BOOST_EXCEPTION_DYNAMIC_TYPEID(*p).type_==ti.type_ );
+                    BOOST_ASSERT( *BOOST_EXCEPTION_DYNAMIC_TYPEID(*p).type_==*ti.type_ );
 #endif
                     return p;
                     }

Is this fix correct?

Thanks in advance.
Pavel Lebedev