[Mono-devel-list] P/Invoke question

Jonathan Pryor jonpryor at vt.edu
Sun Aug 22 10:16:37 EDT 2004

On Sat, 2004-08-21 at 18:56, Julio David Quintana wrote:
> I'm trying to write bindings for rrdtool (librrd.so) and have run across 
> a triple-pointer situation that I'm not quite sure how to handle.
> Code:
> int rrd_graph(int argc, char **argv, char ***prdata, int *xsize, int *ysize)

Well, you could always use IntPtr, or `ref IntPtr', or...

A better question is this: what does `prdata' represent?  Is it an "out"
pointer to an array of strings?  Is it a triply-indirected single
character pointer (unlikely, but possible).  Is it an "in" pointer to a
3-D matrix?

You need to know what you're dealing with to properly P/Invoke with it.

Also important: if `prdata' is an "out" array of strings, what is the
memory allocator?  malloc(3)?  g_malloc()?  GlobalAlloc()? 

For more information, see:

  - The "Managed and Unmanaged Code Integration" guide, in monodoc
    (/Mono Handbook/Advanced Topics/Interoperability/Platform Invoke),
    or http://www.jprl.com/~jon/interop.html.

  - Interop Marshaling at MSDN (beware line wrapping):

 - Jon

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