Mixing /MD and /MT in single dll

Question

I have dll project in Visual Studio 2012, which is compiled with /MT (static multi-threaded runtime library). It also links third-party static lib, also compiled with /MT (library A), no problem so far.

The problem comes with another static lib (library B), which is unfortunatelly compiled with /MD. In my dll, i need to link both and there is no alternative to any of them (and I cannot recompile them with different option). I was able to successfully link everything together, but now I have problems with memory allocation and deletion - sometimes it fails to delete allocated object, sometimes another weird errors occurs. I believe it's caused by mixed memory managment functions, used by different parts of my dll - when new is called, object is created in library B, but when delete is called, it tries to release memory using different set of functions-, but I might be wrong.

So my question is, is this really caused by mixed memory-managment functions? And if so, is there any way to get this work together?

The only solution I think of is to wrap library B in another dll compiled with /MD and then use it from original dll to ensure different memory managment functions will be used. I'm not sure, if this would help and I would like to avoid it.

Answer 1

You already seem to have understood the cause of the problems you're seeing, and it is described on MSDN as follows

If it's really not possible to get all your linked libraries to use the same version of the CRT, then your only possible choice is to avoid passing CRT objects across the boundaries of these modules. Whether or not you can do this with your scenario is entireley dependent on your application. The crucial point in the above article is this sentence:

If you design your DLL so that it passes CRT objects across the boundary or allocates memory and expects it to be freed outside the DLL, you restrict the DLL users to use the same copy of the CRT library as the DLL. The DLL and its users use the same copy of the CRT library only if both are linked with the same version of the CRT DLL.

I know you've stated that it is not possible to obtain or build compatible modules to link to your application but I would recommend that you revisit this exhaustively and avoid mixing different CRT libraries at all costs.