UseDebugLibraries and Wrong Defaults for VC++ Project Properties

Many of the projects I’m working on seem to have wrong default properties in Debug configuration.  For example, ‘Runtime Library’ is explicitly set to /MDd but defaults to /MD. ‘Basic Runtime Checks’ is explicitly set to /RTC1 but defaults to  none. ‘Optimization’ is explicitly set to /Od but defaults to /O2, and so on:

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This recently caused us some trouble, and the investigation results are dumped below.

The direct reason is that these vcxproj’s are missing the ‘UseDebugLibraries’ element, under the ‘Configuration’ PropertyGroup: it should be set to true in Debug and false in Release.   A correct vcxproj should include some elements like –

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
    <ConfigurationType>StaticLibrary</ConfigurationType>
    <UseDebugLibraries>true</UseDebugLibraries>
    <PlatformToolset>v120</PlatformToolset>
    <CharacterSet>Unicode</CharacterSet>
</PropertyGroup>
<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
    <ConfigurationType>StaticLibrary</ConfigurationType>
    <UseDebugLibraries>false</UseDebugLibraries>
    <PlatformToolset>v120</PlatformToolset>
    <CharacterSet>Unicode</CharacterSet>
</PropertyGroup>

Most ‘Configuration’ sub-elements (CharacterSet, ConfigurationType etc.) directly control import of custom property sheets, but UseDebugLibraries doesn’t. Instead, it is expected in various hooks around regular property sheets. For example, Microsoft.Cpp.mfcDynamic.props includes the following –

<ClCompile>
<RuntimeLibrary Condition="'$(UseDebugLibraries)' != 'true'">MultiThreadedDll</RuntimeLibrary>
<RuntimeLibrary Condition="'$(UseDebugLibraries)' == 'true'">MultiThreadedDebugDll</RuntimeLibrary>
</ClCompile>

Why UseDebugLibraries was missing from some libraries and present in others remained a mystery until I noticed that the younger libraries tended to have this element. Indeed, the real culprit is the migration from VS2008- (vcproj format) to VS2010+ (vcxproj/MSBuild format).  MS’s migration code just did not add this element. The generated projects are functional – they just explicitly set every individual compilation switch affected by UseDebugLibraries, which makes it overly verbose and a bit sensitive – especially in the presence of junior devs who tend to stick to defaults…

So every library you have which is 4Y+ old is susceptible to this migration bug, and I suggest you manually add UseDebugLibraries.  If you have a central prop sheet where you can control multiple projects – add it there.

Not much point in reporting this to MS, is there? The chances of a fix are practically zero, and the issue would get equal web-presence here.

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2 Responses to UseDebugLibraries and Wrong Defaults for VC++ Project Properties

  1. John Schroedl says:

    I just checked and that element is missing in some of our projects too. And sure enough, those were migrated from old projects. I’ve seen and wondered about the bold (ie. non-default) highlight on a few of those settings over the years. But since they were correct settings I didn’t investigate more deeply. Thanks Ofek!

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