[Mono-list] Platform invoke for stdarg

[Francis Brosnan Blázquez]

El lun, 15-11-2004 a las 20:54 -0500, Jonathan Pryor escribió:
> On Mon, 2004-11-15 at 20:24 +0100, Francis Brosnan Blázquez wrote:
> > Hi,
> > 
> > I'm trying to do a P/Invoke call for functions such as 
> > 
> > 	void Test(int value, ...); 
> > 
> > But I don't get it working. Is it posible to do a platform invoke for c
> > functions that make use of stdarg api?
> 
> No, and Maybe. :-)
> 
> There is no general way to marshal "..." parameters, which requires that
> all the parameters be passed on the stack -- the Cdecl calling
> convention.  The .NET marshaller can only work with a fixed number of
> arguments.
> 
> However, there are two solutions:
> 
> 1.  Standard overloading: If there is a "reasonable" number of
> parameters you need, you can explicitly specify them as overloads.  I do
> this in Mono.Posix to wrap open(2):
> 
> 	DllImport ("libc", CallingConvention=CallingConvention.Cdecl)
> 	public static extern int open (string pathname, int flags);
> 
> 	DllImport ("libc", CallingConvention=CallingConvention.Cdecl)
> 	public static extern int open (string pathname, int flags, uint mode);
> 
> If you plan on using this code on Windows, you *must* specify
> CallingCOnvention.Cdecl, as the default is Stdcall, which doesn't permit
> variable argument lists.
> 
> Obviously, this is only viable if you have a limited number of potential
> overloads.  Wrapping printf(3) is impractical, as it could result in
> hundreds (thousands?) of overloads.
> 
> 2.  Get creative, take an object[] array, and generate some
> System.Reflection.Emit code which accepts the proper number of
> parameters of the proper type, and invoke the recently generated code.
> IIRC cocoa-sharp does something similar to this for its msg_send
> implementation.  Pro: it works for any argument list.  Con: it's not
> easy.
> 
This solution sounds good. Thanks for your clear reply!
>  - Jon
> 
> 
> 

-- 
Francis Brosnan Blázquez <acinom@bigfoot.com>