Win32-API function calls in VS2005 CLR applications

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R.Kaiser - 04 May 2007 14:13 GMT

I know that I can call Win32 API functions in a Windows forms
application by specifying each function header individually like in

    using namespace System;
    using namespace System::Runtime::InteropServices;

    typedef void* HWND;
    [DllImport("user32.dll", CharSet = CharSet::Ansi)]
    extern "C" int* MessageBox(HWND hWnd, char* pText,
            char* pCaption,unsigned int uType);
    void test_Win32Messagebox_1(void)
    {
    char* pText = "Hello World!";
    char* pCaption = "Platform Invoke Sample";
    MessageBox(0, pText, pCaption, 0);
    }

What I want to know: Is there an easy way to include all headers by
using windows.h or a similar header file:

    extern "C" {
    #include <windows.h>
    }

I tried to combine this #include statement with a DLLImport attribute
like from above, but I did not succeed.

Thanks
Richard

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David Lowndes - 04 May 2007 17:02 GMT

>What I want to know: Is there an easy way to include all headers by
>using windows.h or a similar header file:

Richard,

A C++/CLI program can mix managed/unmanaged calls seamlessly - no need
for anything nasty - so if you need to interface with lots of native
code, C++/CLI is a much cleaner solution.

Dave

Reply to this Message

R.Kaiser - 04 May 2007 17:31 GMT

Hi David,

I was talking of C++/CLI applications. Can you give me an example how to
do it?

Thanks
Richard

David Lowndes schrieb:

>> What I want to know: Is there an easy way to include all headers by
>> using windows.h or a similar header file:
[quoted text clipped - 6 lines]
>
> Dave

Reply to this Message

Carl Daniel [VC++ MVP] - 04 May 2007 18:27 GMT

> Hi David,
>
> I was talking of C++/CLI applications. Can you give me an example how
> to do it?

#pragma managed(push, off)
#include <windows.h>
#pragma managed(pop)

No DllImport attributes are needed. Make sure you're linking with the
appropriate import library(ies) (e.g. kernel32.lib, user32.lib, etc).

-cd

Reply to this Message

R.Kaiser - 04 May 2007 19:06 GMT

Thanks Daniel,

perhaps I confused C++/CLI and CLR applications. I need the Win32-API
functions in a CLR Windows forms application. When I proceed as you
suggested, I get numerous errors like

    Carl DanieC:\Program Files\Microsoft Visual Studio
    8\VC\include\vadefs.h(89) : error C3862: '__va_start':
    cannot compile an unmanaged function with /clr:pure or /clr:safe
#pragma unmanaged is in effect

Or did I confuse something else?

Richard

l [VC++ MVP] schrieb:

>> Hi David,
>>
[quoted text clipped - 9 lines]
>
> -cd

Reply to this Message

Carl Daniel [VC++ MVP] - 04 May 2007 20:29 GMT

> Thanks Daniel,
>
[quoted text clipped - 8 lines]
>
> Or did I confuse something else?

You need to understand what the error message is telling you: You can't
call unmanaged functions, except via P/Invoke, in a "pure" or "safe" CLR
project. You have two choice:

1. Don't use /clr:pure or /clr:safe, just use /clr
2. Don't #include <windows.h> and go back to using DllImportAttribute one
import at a time.

If you take option 1, the resulting application will contain a mixture of
managed and unmanaged code and may not run in certain contexts (e.g. partial
trust environment). Winforms will work fine in a mixed-mode application -
it's entirely a function of the environment in which the application is
deployed whether this option will work for you.

If you take option 2, you're stuck with declaring the functions you need one
by one.

-cd

Reply to this Message

Ben Voigt - 07 May 2007 15:07 GMT

>> Thanks Daniel,
>>
[quoted text clipped - 25 lines]
> If you take option 2, you're stuck with declaring the functions you need
> one by one.

And still won't work in partial trust... because you need native code
permission to use P/Invoke. However you'll get a runtime exception instead
of an outright failure to load.

Best of both worlds... put such calls in a separate unsafe assembly, then
you can still fail gracefully if you don't have native code permission.

> -cd

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Win32-API function calls in VS2005 CLR applications

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