Structure with fieldoffset results in typeloadexception

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VB

Public Structure Foo
<FieldOffset(0)>Public NameLength as Integer '4 Byte
<FieldOffset(4), MarshalAs(UnmanagedType.LPStr, SizeConst:=50)>Public Name As String 'variable name in MBCS
<FieldOffset(54)) Public Age As Integer
End Structure

I would expect the FieldOffsets are okay. But Visual Studio 2013 displays an Error, that the Offset of Age is invalid.

What I have tried:

If I change it to 52, the Error is gone. But I don't know why.

Posted 20-Jul-23 19:58pm

Christian S. (Chris)

Updated 20-Jul-23 20:24pm

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OriginalGriff · Answer 1 · 2023-07-20T20:24:00

I can't check it in VS 2013 - it says my licence is "stale" and it can't retrieve a new one - but if I try it in VS 2022 it works fine converted to C#:

C#

[StructLayout(LayoutKind.Explicit)]
public struct Foo
    {
    [FieldOffset(0)]
    public int NameLength; //4 Byte
    [FieldOffset(4), MarshalAs(UnmanagedType.LPStr, SizeConst = 50)] public string Name; //variable name in MBCS
    [FieldOffset(54)] public int Age;
    }

But in VB, it gives me an error that a ">" is missing:

VB

<FieldOffset(54)) Public Age As Integer
                ^

Which says that the code you are getting the error from isn;t the code you showed us - that won't compile so even if you did change it to "52" you'd still get an error.
Correct it, and I get no errors at all:

VB

Public Structure Foo
    <FieldOffset(0)> Public NameLength As Integer '4 Byte
    <FieldOffset(4), MarshalAs(UnmanagedType.LPStr, SizeConst:=50)> Public Name As String 'variable name in MBCS
    <FieldOffset(54)> Public Age As Integer
End Structure