Question

I have a managed C++ dll which uses a unmanaged C++ lib. I’ve added the lib file in the managed project’s “Additional Dependencies”. Unfortunately I get a dozen of std::locale already defined in msvcprtd.lib linking errors.

Any idea? Do I have to build both as dll and link them together?

Answer 1

You probably need to change the runtime library setting for one of your projects so that they are both the same. The “Multi-threaded Debug DLL” option in the runtime library settings means that your project will be linked against the DLL version of the runtime lirary, not that your project is a DLL. Where-as “Multi-Threaded Debug” means it will link against a .lib version of the standard library.

When you link together 2 projects that use different settings, then they end up with duplicate references. One reference from the static runtime library, and one from the DLL runtime library. This is the source of your errors.

Which setting you should pick depends on whether you want to distribute the runtime DLLs with your project (or count on the user already having them). If you want to go for this option, select the DLL runtime library, otherwise select the non-DLL version. The down side of the non-DLL version is that all the runtime library code will be embedded in your DLL/EXE, which will increase it’s size.

EDIT: Actually, looking into it a bit more. This link indicates that with CLR projects (which I suspect yours is, being managed C++) you can’t use the static linked option, so you need to use the “Multi-threaded Debug DLL” option for both.