[llvm-dev] Disabling inline compilation (Clang with VS2019)

[Dimitry Andric via llvm-dev]

On 22 Sep 2021, at 14:22, John Emmas via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi there - I first asked this question over on clang-users but I got advised to ask it here (sorry about the length...)
> 
> I'm a VS2019 user and I've been trying to switch it here to use Clang as the compiler, rather than MSVC. But I seem to have hit a common problem.  Consider the following code:-
> 
> #if defined (BUILDING_DLL)
>  #define DLL_API __declspec(dllexport)
> #else
>  #define DLL_API __declspec(dllimport)
> #endif
> 
> namespace Gtkmm2ext {
> 
>  class DLL_API Keyboard
>  {
>    public:
>      Keyboard ();
>      ~Keyboard ();
> 
>      static Keyboard& get_keyboard() { return *_the_keyboard; }
> 
>    protected:
>      static Keyboard* _the_keyboard;
>  };
> 
> } /* namespace */
> 
> The above code is from a DLL which gets used by an exe.  The DLL compiles and links just fine and the exe compiles.  But when I try to link the exe, Clang's linker complains that it can't find '_the_keyboard'

As far as I understand it, if you specify __declspec(dllexport) for a whole class, then *all* members, including statics, get explicitly exported in the DLL image.

I.e. it is as if you had manually specified __declspec(dllexport) to each and every member. I don't know if there is any way to override that for just a single class member, for example as with gcc you could add a __attribute__((visibility("hidden"))) to one of them.

So maybe you can selectively add DLL_API to those class members that you need exported, as described here:
https://docs.microsoft.com/en-us/cpp/cpp/using-dllimport-and-dllexport-in-cpp-classes?view=msvc-160#_pluslang_using_dllimport_and_dllexport_in_c2b2bselectivememberimportexport

-Dimitry

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