Why does LayoutKind.Sequential work differently if a struct contains a DateTime field?

Question

Why does LayoutKind.Sequential work differently if a struct contains a DateTime field?

Consider the following code (a console app which must be compiled with \"unsaf

Answer 1

If you're going to interop with C/C++, I would always be specific with the StructLayout. Instead of Sequential, I would go with Explicit, and specify each position with FieldOffset. In addition, add your Pack variable.

[StructLayout(LayoutKind.Explicit, Pack=1, CharSet=CharSet.Unicode)]
public struct Inner
{
    [FieldOffset(0)]
    public byte First;
    [FieldOffset(1)]
    public double NotFirst;
    [FieldOffset(9)]
    public DateTime WTF;
}

It sounds like DateTime can't be Marshaled anyhow, only to a string (bingle Marshal DateTime).

The Pack variable is especially important in C++ code that might be compiled on different systems that have different word sizes.

I would also ignore the addresses that can be seen when using unsafe code. It doesn't really matter what the compiler does as long as the Marshaling is correct.