Re: unmanaged structure layout error

Private System.String _name = New String(" "c, 70)



John Warner


> -----Original Message-----
> From: Discussion of advanced .NET topics. [mailto:ADVANCED-
> [email protected]] On Behalf Of Mike Andrews
> Sent: Wednesday, November 11, 2009 2:46 PM
> To: [email protected]
> Subject: Re: [ADVANCED-DOTNET] unmanaged structure layout error
> 
> Oh, ok.  I get it.
> 
> I kinda thought that might be it as well except that in .NET there is no
> specific size for a string.  That's what I thought the MarshalAs
attribute
> was for; that I'm saying that the field starts and byte index 64 and
> continues for 70 bytes.  That puts it at byte 134 for the next offest.
The
> previous offset is 64 - 133.  I've tried specifying 133 and 135 or the
> offset for the _address1 but nothing seems to work.
> 
> On Wed, Nov 11, 2009 at 1:38 PM, John Warner <[email protected]> wrote:
> 
> > 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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