[Mono-devel-list] Calling Native C api - Marshalling issue.
YogendraT at ami.com
Thu Jul 28 12:31:28 EDT 2005
Thanks Massi & Zoltan.
It works after removing the ref. As Zoltan said, by defualt classed are
passed as reference to unmanaged code.
From: Massimiliano Mantione
To: Yogendra Thakur
Cc: 'mono-devel-list at lists.ximian.com '
Sent: 7/28/05 11:17 AM
Subject: Re: [Mono-devel-list] Calling Native C api - Marshalling issue.
On Thu, 2005-07-28 at 10:15 -0400, Yogendra Thakur wrote:
> I am getting problem while executing the c library function from C#.
> //Define equivalent class to MyData structure
> public class CSMyData
either should be a struct, not a class...
> //Import the dll and define C function.
> [DllImport ("mylibrary.dll", EntryPoint="DoSomeOperation")]
> static extern Int32 OperateData( ref CSMyData pData);
> //Other way of defining
> //static extern Int32 OperateData( [In,Out] CSMyData pData);
...or you should omit the "ref" (or the "[In,Out]").
With these modification it works.
The issue is that if CSMyData is a struct, then the "ref" (or the
"[In,Out]") is needed to get the address of the struct.
But if CSMyData is a class, marshalling converts it correctly.
I am no marshalling expert, but I think that if you put the "ref"
you pass the address of the object reference :-)
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