Visual Studio C++ dll library crashes in Qt application

Question

I have a problem sharing "std::string" data between MS Visual C++ DLL library and Qt program.

What I have are:

• DLL library written in Visual C++ 2010 Express, which exports one method:

  extern "C" __declspec(dllexport) int Init(ITest* commandTest);
  

• Abstract interface "ITest" and a class implementing it:

  class CTest: public ITest
  {
  public:
      CTest();
      virtual ~CTest();
      virtual void getVersion(std::string & version) const;
  };
  

• Qt GUI application that needs to:

  * load the DLL dynamically
  * instantiate CTest and pass it to exported Init method.
  

In DLL's "Init" a "CTest::getVersion()" method is called. I'd expect it would get the "&version" string filled in. What I get instead are crashes on the line when I fill "&version" with new string.

What I already did:

• downloaded "Qt libraries 4.8.3 for Windows (VS 2010, 235 MB)" from http://qt-project.org/downloads, installed it and selected it in QtCreator's project settings.

• in QtCreator switched from MinGW toolchain to the one installed with MS Visual Studio 2010 Express.

  I thought that it will overcome the problem , because I used Qt libraries compiled with VS 2010 and the Qt GUI was also compiled with VS C++ toolchain then. Unfortunately the problem was not gone, so I tried the last step:

• created Win32 Console application in Visual Studio, loaded my DLL via LoadLibrary, used "Init" method the same way as I did in Qt GUI... and it worked!!

Small observation

In "CTest::getVersion()" I am printing this "version" string passed by reference to the console. When using VS C++ console app as a host it is printed out correctly. When using Qt app - the "version" string is printed with some garbage around (e.g. ┌►☻qwerty27)

This makes me think that ABI of Qt app and my DLL is still incompatible, even when using Qt VS 2010 libraries mentioned above.

Questions:

• Is using Qt libraries for Windows (VS 2010) and Visual Studio toolchain not enough to overcome ABI compatibility issues?
• Does it mean I should compile the Qt framework on my own?
• Please help - any ideas are welcome...