MSVC_RUNTIME_LIBRARY defaults to dynamic linking for static libraries?!

Code
, ,
1

Hi,

I use CMake with CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS to automatically generate both a shared dll and static .lib library on Windows when building with MSVC. I found out yesterday that the static .lib uses dynamic linking and hence requires using the /MD compiler option (instead of /MT). This is a bit surprising to me, why does it not use static linking for static .lib files?

In the CMake documentation (https://cmake.org/cmake/help/latest/prop_tgt/MSVC_RUNTIME_LIBRARY.html) I found:

MSVC_RUNTIME_LIBRARY: “If this property is not set then CMake uses the default value MultiThreaded$<$<CONFIG:Debug>:Debug>DLL to select a MSVC runtime library.”

What is the reason for using MultiThreadedDLL by default (instead of MultiThreaded) for static .lib files? Maybe that is a good choice and I just fail to understand…

2

Because you cannot mix them well. Compiling every static library with the static runtime is problematic when linking static and dynamic libraries into an executable.

3

OK, thanks that’s exactly what I wanted to know.

4

The .lib is not a static library here. It is an import library for the .dll library (which contains the actual runtime code).

5

Yes, I know. But in my project I have renamed that file to .dll.lib and I also generate a true static .lib library. And this static .lib is linked using /MD by default. (Which is totally fine, I just wanted to understand why /MD is used instead of /MT)

6

You can set the MSVC_RUNTIME_LIBRARY target property on the target to switch which variant of the runtime is used.

7

Yes thanks, based on the feedback from this thread I have added this as an option this morning: Add MSVC_CRT_STATIC option · kimwalisch/primesieve@a3a755f · GitHub