Re: A question on __declspec(dllimport) and the Windows APIs.

From:
"Doug Harrison [MVP]" <dsh@mvps.org>
Newsgroups:
microsoft.public.vc.mfc
Date:
Tue, 07 Aug 2007 23:35:36 -0500
Message-ID:
<rqhib3tdaoq5qe5qidvgk7dgm3arrb1vu5@4ax.com>
On Tue, 07 Aug 2007 21:16:30 -0700, xmllmx <xmllmx@gmail.com> wrote:

In chapter 19 of Jeff's classic book "Programming Applications for
Microsoft Windows", there is a paragraph as follows:

"What Importing Really Means

The previous section introduced the _ _declspec(dllimport) modifier.
When you import a symbol, you do not have to use the _
_declspec(dllimport) keyword-you can simply use the standard C extern
keyword. However, the compiler can produce slightly more efficient
code if it knows ahead of time that the symbol you are referencing
will be imported from a DLL's .lib file. So I highly recommend that
you use the _ _declspec(dllimport) keyword for imported function and
data symbols. Microsoft does this for you when you call any of the
standard Windows functions."

Note the last statement "Microsoft does this for you when you call any
of the standard Windows functions." I think it is without any support
of facts.

If his statement is true, then the declaration of an API function
(say, API GetWindow(...)) should be like this:

__declspec(dllimport) HWND __stdcall GetWindow(HWND hWnd, UINT uCmd);

However, Microsoft didn't do this. In the winuser.h, I found the
function is declared:

WINUSERAPI HWND WINAPI GetWindow(__in HWND hWnd, __in UINT uCmd);

Which is identical to HWND __stdcall GetWindow(HWND hWnd, UINT uCmd);

Who is wrong???


Compile with -P and examine the .i file that is produced. I get:

__declspec(dllimport)
HWND
__stdcall
GetWindow(
         HWND hWnd,
         UINT uCmd);

Rule of thumb: When in doubt, bet on Richter. :)

--
Doug Harrison
Visual C++ MVP

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