Re: unmanaged structure layout error

I specified the CharSet = CharSet.Ansi in the StructLayout attribute as well
so it should work as it shouldn't be trying to interpret the data as
Unicode.
I'm not trying to model a union so I guess I'll stick with
LayoutKind.Sequential since it works.

On Wed, Nov 11, 2009 at 2:03 PM, Richard Blewett <[email protected]>wrote:

> At a guess the string was Unicode (TStr can be ansi or Unicode strings) and
> so the null terminated string overran the next field
>
> LayoutKind.Sequential will do the right thing most of the time unless you
> are trying to model unions etc
>
> Rich
>
> -----Original Message-----
> From: Discussion of advanced .NET topics.
> [mailto:[email protected]] On Behalf Of Mike Andrews
>  Sent: 11 November 2009 19:55
> To: [email protected]
> Subject: Re: [ADVANCED-DOTNET] unmanaged structure layout error
>
> I just tried something different and it seemed to work.
>
> I remove the LayoutKind.Explicit and specified LayoutKind.Sequential.  I
> then removed the FieldOffset attribute and that seemd to fix the problem.
>
> I would still like to know why having explicit field offsets causes an
> exception when the type is loaded.  It really doesn't make any sense to me.
>
> On Wed, Nov 11, 2009 at 1:46 PM, Mike Andrews
> <[email protected]>wrote:
>
> > 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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