[CMake] Force MSVC runtime for debug builds

[Mueller-Roemer, Johannes Sebastian]

I agree that CMake should not be defining _DEBUG explicitly, as it is used by Microsoft’s headers to match the chosen runtime.
Maybe this warrants a bug report on gitlab.

From: CMake [mailto:cmake-bounces at cmake.org] On Behalf Of Kim Kryger
Sent: Monday, November 14, 2016 22:05
To: Stephan Menzel <stephan.menzel at gmail.com>
Cc: cmake <cmake at cmake.org>
Subject: Re: [CMake] Force MSVC runtime for debug builds

I ran into this today. I tried to use /MD to link against a custom md library, but because _DEBUG was defined *by CMake* I couldn't use it out of the box.

Why is CMake defining _DEBUG for MSVC projects anyways? _DEBUG is automatically defined when using /MDd, and I don't believe it should be defining it itself. I've had to remove it for multiple projects because it's making assumptions as to what I want defined.


Default for CMAKE_CXX_FLAGS_DEBUG_INIT
/D_DEBUG /MDd /Zi /Ob0 /Od /RTC1

I don't think that first define should be there.


Reference:
https://github.com/Kitware/CMake/blob/5d29506811c5b75ae48e12de6c317f6440874215/Modules/Platform/Windows-MSVC.cmake#L294
https://msdn.microsoft.com/en-us/library/0b98s6w8.aspx


On Fri, Nov 11, 2016 at 9:42 AM, Stephan Menzel <stephan.menzel at gmail.com<mailto:stephan.menzel at gmail.com>> wrote:

On Tue, Nov 8, 2016 at 4:21 PM, <clinton at elemtech.com<mailto:clinton at elemtech.com>> wrote:
If you are going to use /MD instead of /MDd, then you probably also need to remove the _DEBUG preprocessor flag.
IIRC, I've seen cases where defining _DEBUG includes symbols only defined by the debug runtimes.

Clint

What a surprise. Removing _DEBUG did the trick. I was under the impression _DEBUG only controls Microsoft STL impl's debug iterator stuff but apparently it also makes the resulting exe link with /MD rather than /MDd. Guess that was wrong.

So yes, problem solved.

Thank you!

Stephan

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