Re: unmanaged structure layout error

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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