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.NET Forum / Languages / VB.NET / October 2007Declare Sub XXX Lib "X.dll" (Structure vs Class) ...
Hello - I have an Ada *.dll that is called from withing VB.NET. The following works ... Public Declare Sub XXX Lib "X.dll" (ByRef XArgument As XStructure) <StructLayout(LayoutKind.Explicit)> _ Structure XStructure <FieldOffset(0)> Dim A As Single <FieldOffset(4)> Dim B As Single ... End Structure ... but I would like to use a Class to utilize inheritance. Here is what does not work ... Public Declare Sub XXX Lib "X.dll" (ByRef XArgument As XClassBase) Class XClassBase End Class <StructLayout(LayoutKind.Explicit)> _ Class XClassDerived Inherits XClassBase <FieldOffset(0)> Dim A As Single <FieldOffset(4)> Dim B As Single ... End Class ... when I call it using ... Dim lDummy as New XClassDerived XXX(CType(lDummy, XClassDerived)) I assume that the Class stores some additional data that confuses the interface to teh X.dll? Is there any way to make this work??? Thanks! Joe > Dim lDummy as New XClassDerived > XXX(CType(lDummy, XClassDerived)) > > I assume that the Class stores some additional data that confuses > the interface to teh X.dll? No. A structure is a value type. A class is a reference type. Using ByRef, the reference to the passed value is passed. Using ByVal.... wait... http://groups.google.com/group/microsoft.public.dotnet.languages.vb/msg/41e83beb 9988aabf > Is there any way to make this work??? Change it to ByVal: (ByVal XArgument As XClassBase) Armin Hello - Thanks for the information! Using ByVal will not make it abort anymore but the function in the X.dll that is called modifies the fields of the data passed in. So I need to use ByRef to get to the modified values. Is there any way to make this work with ByRef? Thanks, Joe > > Dim lDummy as New XClassDerived > > XXX(CType(lDummy, XClassDerived)) [quoted text clipped - 12 lines] > > Armin Passing a reference type byval does allow the function to change the passed type. ByVal of a reference type, passes the reference, allowing the routine to change the object that the reference points to. ByRef of a reference type, passes a reference to the reference, allowing the routine to change the reference!  SignatureTerry > Hello - > [quoted text clipped - 24 lines] > > > > Armin Yep ... that was my point. I need this to work with ByRef ... any ideas? Thanks! Joe > Passing a reference type byval does allow the function to change the passed > type. ByVal of a reference type, passes the reference, allowing the routine [quoted text clipped - 34 lines] > > - Show quoted text - > Yep ... that was my point. I need this to work with ByRef ... any > ideas? I *think* Terry was trying to say that you can change your declaration to ByVal and you will still be able to change the fields of the param in question. ByVal only prevents you from assigning a new object to the param. -- Rory you had said ..."but the function in the X.dll that is called modifies the fields of the data passed in" And I am saying, passing a reference type byval DOES allow that. When passing a reference type byval, a copy of the REFERENCE (not the object the reference points to) is passed to the function so that there are now 2 references to the SAME object. Now having said all that, I am not familiar with Ada, so I don't know if that presents any additional complications. SignatureTerry > Yep ... that was my point. I need this to work with ByRef ... any > ideas? [quoted text clipped - 40 lines] > > > > - Show quoted text - Hello - Sorry guys ... I guess I did not pay attention when I read this. I remember the concept of passing in a copy of the reference from C++. I did not create the *.dll but I can talk to the person who did to see whether this can be done in Ada. Thanks! Joe > you had said ..."but the function in the X.dll that is called modifies the > fields of the data passed in" [quoted text clipped - 53 lines] > > - Show quoted text - No you don't need ByRef. In either case the called routine can modify the contents of the class or structure. With ByRef the called routine can allocate a new instance of the class and change the reference in the caller. With ByVal the caller's reference can't change. >Hello - > [quoted text clipped - 24 lines] >> >> Armin Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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