Unable to pass std::wstring across DLL

Question

I\'ve set up a project in Visual Studio 2010 to write unit tests against an existing MFC DLL. I\'m using a single-header unit test framework, and linked to the MFC DLL\'s li

Answer 1

You should check that both the EXE and the DLL are dynamically linked with the same debug CRT (/MDd compiler option). Make sure that also other settings like _HAS_ITERATOR_DEBUGGING are the same for both the EXE and the DLL.

(A shortcut could be to just use const wchar_t* instead of std::wstring at the class interface, and just build a std::wstring from the raw pointer inside constructor's body).

EDIT: You confirmed that CRT mismatch (i.e. EXE built with /MD vs. DLL built with /MDd) was the problem. The fact is that the same class name std::wstring means two different classes in debug builds (/MDd) and in release builds (/MD). In fact, in debug builds there can be additional mechanics inside the class implementation to help debugging; this mechanics can introduce inefficiencies, so it's removed in release builds. So, the internal structure of debug build's std::wstring is different from release build's std::wstring (e.g. if you try to print the raw sizeof of std::wstring instances, you can find different numbers in release builds and debug builds). So, the EXE built with /MD was expecting release-build's std::wstring; instead the DLL built with /MDd was expecting debug-build's std::wstring: there is a mismatch between these two expectations (one module is expecting class X but the other module is giving class Y) and so you have a crash.