mixing code compiled with /MT and /MD

Question

I have a large body of code, compiled with /MT (i.e. expecting to statically link against the CRT). I need to combine this with a static third-party library, which has been built with /MD (i.e. expecting to link the CRT dynamically).

Is it theoretically possible to link the two into one executable without recompiling either?

If I link with /nodefaultlib:msvcrt, I end up with a small number of undefined references to things like __imp__wgetenv. I'm tempted to try implementing those functions in my own code, forwarding to wgetenv, etc. Is that worth trying, or will I run straight into the next problem?

Unfortunately I'm Forbidden from taking the easy option of packing the thirdparty code into a separate DLL :-/

Answer 1

No. /MT and /MD are mutually exclusive.

All modules passed to a given invocation of the linker must have been compiled with the same run-time library compiler option (/MD, /MT, /LD).

Source

Answer 2

I found such solution in OpenSSL sources: All obj files of the library are compiled with combination: /MT /Zl. As author described, such combination allows to build static library with ability to compile with applications either dynamic CRT (/MD) or static CRT (/MT).

Answer 3

I faced similar situation where in I had two libraries one was built with MT and another one with MD. I had to build an executable which uses functionalities from both the libraries. The library built as MD was third party thus I couldn't rebuilt it and library built as MT has many dependencies and to built all of them as MD is a big pain. I was getting error from the third party config header file which made it mandatory to built the executable as MD. I was looking for the easy way of packaging third party dll as a separate dll as mentioned in question. However, I couldn't find enough explanation online on this easy way. Hence my two cents below. The following is the way I circumvent it

1. I built another .dll which acted as an interface. This interface basically wrapped all api calls that was made to third party dll. The header file for this interface did not include any header file from third party dll rather all those header files were included in the interface.cpp file. Interface as you expect was built as MD.

2. Now In my main.cpp file I included this interface header file to make all the calls to third party dll through the interface.

3. Extra care has to be taken in passing arguments to the interface. Basic variables like int,bool etc can be passed as value. However any class or structure needs to be passed as const reference to avoid heap corruption. This is applicable to even string.

Happy to share more details if it is not clear!