[cfe-dev] CLang compiling windows.h from the Windows SDK

[Dimitry Andric]

On 2010-08-09 00:13, Christopher Jefferson wrote:
>>> 3. CLang doesn't like:
>>>    template<typename T> void** IID_PPV_ARGS_Helper(T** pp)
>>>    {
>>>       static_cast<IUnknown*>(*pp);            <=== clang error:
>>> unknown type name 'IUnknown'
>>>       return reinterpret_cast<void**>(pp);
>>>    }
>>> Note that 'IUnknown' is actually undefined at this point but MSVC accept it.
>>
>> Is it truly undeclared, or is it some kind of magic type? The former is very hard to deal with. 
> 
> It is truly undeclared, this is due to windows being lax on what it accepts in templates. However, with some careful consideration, clang could possibly consider making it a magic type, if there is only a very small number of such hacks required to parse windows.h. I haven't done a careful analysis of how many such examples there are.

Ehm, I have a file "Unknwn.h" in my Microsoft SDK dir, that defines
IUnknown as:

  MIDL_INTERFACE("00000000-0000-0000-C000-000000000046")
  IUnknown
  {
  public:
  [...]

where MIDL_INTERFACE basically means "struct" (from MqOaI.h):

  #ifndef MIDL_INTERFACE
  #if _MSC_VER >= 1100
  #define MIDL_INTERFACE(x)   struct __declspec(uuid(x)) __declspec(novtable)
  #else
  #define MIDL_INTERFACE(x)   struct
  #endif //_MSC_VER
  #endif //MIDL_INTERFACE

The only declaration in Unknwn.h that I can't parse is this IUnknown
forward declaration, again in Unknwn.h:

  #ifndef __IUnknown_FWD_DEFINED__
  #define __IUnknown_FWD_DEFINED__
  typedef interface IUnknown IUnknown;
  #endif 	/* __IUnknown_FWD_DEFINED__ */

That "interface" keyword is probably something Microsoft-specific...