Re: unmanaged structure layout error

Please don't mistake my question for knowledge! Just given the error
message it seems to me the problem is in the last three fields and I
suspect really the last two. String_name must be going further than offset
134.

But again, make no mistake my question here is not a show of knowledge
just a guess from the peanut gallery (if you are old enough to know that
one)

John Warner


> -----Original Message-----
> From: Discussion of advanced .NET topics. [mailto:ADVANCED-
> [email protected]] On Behalf Of Mike Andrews
> Sent: Wednesday, November 11, 2009 2:35 PM
> To: [email protected]
> Subject: Re: [ADVANCED-DOTNET] unmanaged structure layout error
> 
> I'm not sure I understand.
> I assumed that by placing [MarshalAs(UnmanagedType.ByValTStr, SizeConst
> =
> 70)] over the field that it would read the next 70 bytes as a string.
> 
> But that still doesn't explain why the runtime is crying when it tries
to
> load the type.
> 
> On Wed, Nov 11, 2009 at 1:26 PM, John Warner <[email protected]> wrote:
> 
> > Does the string class need more space than the data it contains?
> >
> > String_name
> >
> > John Warner
> >
> >
> > > -----Original Message-----
> > > From: Discussion of advanced .NET topics. [mailto:ADVANCED-
> > > [email protected]] On Behalf Of Mike Andrews
> > > Sent: Wednesday, November 11, 2009 2:04 PM
> > > To: [email protected]
> > > Subject: [ADVANCED-DOTNET] unmanaged structure layout error
> > >
> > > I'm having a problem with an unmanaged structure.
> > >
> > > I'm getting this error message when the system tries to load the
type:
> > >
> > > *Could not load type '_S' from assembly '...' because it contains an
> > object
> > > field at offset 134 that is incorrectly aligned or overlapped by a
> > > non-object field.*
> > >
> > > For the life of me I cannot figure this out why this is failing.
> > > I've set the byte packing to 1 which means that there is no padding
> > between
> > > bytes.  I've also explicitly specified each field offset.
> > >
> > > Below is the structure that I have declared.  It's only a partial
> > structure
> > > and I removed all the properties for brevity.  Also there's more
members
> > but
> > > the last field is where the error is occurring.  Also, if I remove
the
> > last
> > > field it works.  When I add it back it fails.
> > >
> > > Any suggestions?
> > >
> > > Thanks,
> > > Mike
> > >
> > > [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi, Pack =
1)]
> > > private struct _S {
> > >     [FieldOffset(0)]
> > >     private System.Double _height;
> > >     [FieldOffset(8)]
> > >     private System.Double _width;
> > >     [FieldOffset(16)]
> > >     private System.Double _depth;
> > >     [FieldOffset(24)]
> > >     private System.Double _a;
> > >     [FieldOffset(32)]
> > >     [MarshalAs(UnmanagedType.ByValArray, SizeConst = 24)]
> > >     private System.Byte[] _u1;
> > >     [FieldOffset(56)]
> > >     private System.UInt16 _number;
> > >     [FieldOffset(58)]
> > >     private System.UInt16 _d;
> > >     [FieldOffset(60)]
> > >     [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
> > >     private System.Byte[] _u2;
> > >     [FieldOffset(64)]
> > >     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 70)]
> > >     private System.String _name;
> > >     [FieldOffset(134)]
> > >     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 33)]
> > >     private System.String _address1;
> > >
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