On 08/25/03 Patrick Hartling wrote:
I am experimenting with mapping C++ to C# via P/Invoke and Mono 0.26 on Red Hat 8.0, and I have run into something odd when a native function returns a C++ object by value. From the way it is behaving, it appears that something is going wrong in the allocation of memory on the stack for the return value.
I have attached some code that demonstrates the problem. My intent is to use a custom marshaler to make a copy of the return value object in a freshly allocated C# object reference. (The validity of this technique is what I am evaluating, so it's possible I am going down the wrong road with this.)
[...]
[DllImport("return_copy")] [return : MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(ReferenceDataMarshaler))] private static extern ReferenceData Marshal_getReferenceCopy(IntPtr instPtr);
Does your code work under the MS runtime?
As you point out below, there was a mismatch in the code, but with a modification, it did work with the MS runtime. It doesn't fix the problems with Mono, unfortunately.
I'm not sure it's supposed to work. ReferenceData in C# is a class, so by default the marshal code in mono (check metadata/marshal.c) assumes the unmanaged function returns a pointer. The C++ code, though returns the data by value, so you have a mismatch. You may try to define a C# struct that matches ReferenceData and use that as the type returned from Marshal_getReferenceCopy(). In a wrapper you create a ReferenceData obj and copy the fields from the struct.
That sounds like a good idea. Thanks for the tip.
-Patrick
-- Patrick L. Hartling | Research Assistant, VRAC [EMAIL PROTECTED] | 2624 Howe Hall: 1.515.294.4916 http://www.137.org/patrick/ | http://www.vrac.iastate.edu/
_______________________________________________ Mono-list maillist - [EMAIL PROTECTED] http://lists.ximian.com/mailman/listinfo/mono-list
