[Mono-list] Win32 API problems

[A Rafael D Teixeira]

>From: Paolo Molaro <lupus@ximian.com>
>
>On 06/13/02 Adiraj, Sarat wrote:
> > [DllImport("user32")]
> > public static extern int MessageBoxA(int hWnd,
> > String pText ,
> > String pCaption ,
> > int uType);
>
>What is the signature of the MessageBoxA() function in C code?
>There may be two issues:
>1) we currently marshal strings as utf8 char*. MessageBoxA() for all I
>know may want UTF-16 (though I guess the 'A' is for ASCII?).

MessageBoxA accepts  8-bit ANSI (with MBCS = Multibyte Character Set ), 
MessageBoxW accepts 16-bit UTF-16

BUT you should follow this example:
<SNIP>
using System.Runtime.InteropServices;

public class Win32
{
   [DllImport("user32.dll", CharSet=CharSet.Auto)]
   public static extern int MessageBox(int hWnd, String text,
                     String caption, uint type);
}
</SNIP>

And let the marshaller do the string type matching or translation, by 
looking at the Charset property of the DllImportAttribute.

Or if really needed:

<SNIP>
public class Win32
{
  [DllImport("user32.dll", CharSet=CharSet.Ansi)]
  public static extern int MessageBoxA(int hWnd, String text,
			String caption, uint type);
}
</SNIP>

I tested both in VS.NET

>2) The call convention: we call the P/Invoke function with th cdecl call
>convention by default. It may be that MessageBoxA() uses another
>convention.
>

AFAIK, the calling convention of every Win32 API is __stdcall (function pops 
its parameters from stack), except for a few APIs with a variable number of 
parameters (MSVC automatically call them as __cdecl). There´s also some 
name-mangling

int MessageBoxA(int hWnd, String text,
			String caption, uint type)
is decorated as

_MessageBoxA@16

The '16'-part is because it expects 16 bytes to be pushed in the stack for 
its parameters...

Happy hackings...

Rafael Teixeira
Brazilian Developer


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