[Mono-list] PInvoke & Marshaling problem

[Marcus]

I reported this bug a couple days ago:

http://bugs.ximian.com/show_bug.cgi?id=61134

On Saturday 03 July 2004 4:06 pm, Kai Reichert wrote:
> Hi!
>
> I want to pass an array of bytes to a method compiled in c/c++.
>
> The first naiv method works and looks like this :
>
>  - ---------------------
>   xx.c :
>
> void takeArray( unsigned char array[] ){
>   /* do something useful with it */
> }
>
>   xy.cs :
>
>   [ DllImport(myclib.so) ]
>   static extern void takeArray(  byte[] array  );
>   byte[] array = new byte[10];
>   takeArray( array );
>  - --------------------------
>
> O.K., this one works perfectly.
> But now consider you have a c-method that takes the array as
>
>   takeArray( const void *pointer )
>
> YES, it makes sense, e.g. the OpenGL method glTexImage2D.
>
> Since all structures are passed by reference the parameter of the method is
> just the pointer to the beginning of the structure in memory. so I only
> need a way to access this pointer.
>
> my aproach was the following :
>
> takeArray ( GCHandle.Alloc( array,
> GCHandleType.Pinned).AddrOfPinnedObject() );
>
> BUT this method invocation is not associated with the right piece of memory
> that the subsequent c-method gets :-)
>
> Yes I know that Mono has a garbage collection and there are mechanisms in
> the runtimes that copy memory from managed to unmanaged. This wouldn't be a
> problem ...
>
> I just want to know why it is not possible to pass
>
>   System.IntPtr   --C-->  const void*
> since
>   byte[]    --C--> unsigned char array[]
> works ;-)
>
>
> Thx for reading boring PInvoke problems :-)
>
> Kai
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