The problem manifested itself during Batch Build with errors indicating that Debug libraries were being linked into Release builds. For example, these errors happen if you are using STL:
Core.lib(HttpHelpers.obj) : error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '2' doesn't match value '0' in Activation.obj
MSVCRTD.lib(MSVCR100D.dll) : error LNK2005: _strcspn already defined in libcmt.lib(strcspn.obj)
I've also seen these errors for vanilla MFC projects:
msvcrtd.lib(ti_inst.obj) : error LNK2005: "private: __thiscall type_info::type_info(class type_info const &)" (??0type_info@@AAE@ABV0@@Z) already defined in libcmt.lib(typinfo.obj)
msvcrtd.lib(ti_inst.obj) : error LNK2005: "private: class type_info & __thiscall type_info::operator=(class type_info const &)" (??4type_info@@AAEAAV0@ABV0@@Z) already defined in libcmt.lib(typinfo.obj)
Visual Studio 2010 has multiple ways of specifying dependencies. The actual effect of each setting and settings' interdependence does not appear to be officially documented, although there is some information at http://msdnrss.thecoderblogs.com/2010/02/16/project-settings-changes-with-vs2010/ and at http://blogs.msdn.com/vcblog/archive/2010/03/02/visual-studio-2010-c-project-upgrade-guide.aspx.
The first way of specifying dependencies continues from previous versions of Visual Studio in Project | Project Dependencies. However, unlike earlier versions of Visual Studio, this only affects project build order, not dependency library linking. Also, this only affects project build order in the IDE. It does not affect project build order in MSBUILD. Therefore, you need to configure that page, but it's useless for command line builds. Changes on this page are reflected in the .sln file.
The real action is now on the Framework and References tab in the project properties. This tab used to be exclusively for .Net dependencies, but now it's been expanded for C++ dependencies. When I looked at this page for my project, it looked like this:
There are a couple of things to notice. First, the Configuration in the top left is grayed out. The Debug/Release settings do not apply to the Framework and References page. Second, you'll notice that the Full Path in the properties on the right points to the Debug build. In other words, the Debug library is always linked, even in the Release build. I've blogged about this problem in the past with .Net libraries, but this is pretty fundamental for C++ libraries.
I first thought that the solution was to set Reference Assembly Output to False. However, after reading the blog of one of the Microsoft Program Managers and following up with him, he said that the Reference Assembly Output option is only for managed libraries and does not do anything for native libraries. He said that the behavior I'm seeing is anamolous and that it shouldn't be happening.
[Update 7/18/2010] I have confirmed that this problem only happens with Batch Build. The problem doesn't happen if you explicitly choose a configuration, nor does the problem happen when running MSBUILD from the command line.
I have opened a bug report on Microsoft Connect. Please vote for it at:
[Update 7/18/2010] Microsoft has reproduced the problem, but has decided not to fix it. If you are reading this, PLEASE let them you that fixing this problem is important to you!