Re: 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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