How do I define the TBBUTTON struct in C#?

Question

Greetings all,

The TBBUTTON struct is defined on MSDN as follows:

typedef struct {
  int       iBitmap;
  int       idCommand;
  BYTE      fsState;
  BYTE      fsStyle;
#ifdef _WIN64
  BYTE      bReserved[6];
#else 
#if defined(_WIN32)
  BYTE      bReserved[2];
#endif 
#endif 
  DWORD_PTR dwData;
  INT_PTR   iString;
} TBBUTTON, *PTBBUTTON, *LPTBBUTTON;

I need to do some interop in C# using this struct. How do I replicate this monster so that it's defined correctly when compiled for AnyCPU? Google is apparently full of dangerous misinformation!

Answer 1

Ahah, I knew there had to be a way. And here it is:

[StructLayout(LayoutKind.Sequential)]
public struct TBBUTTON {
    public int iBitmap;
    public int idCommand;
    [StructLayout(LayoutKind.Explicit)]
    private struct TBBUTTON_U {
        [FieldOffset(0)] public byte fsState;
        [FieldOffset(1)] public byte fsStyle;
        [FieldOffset(0)] private IntPtr bReserved;
    }
    private TBBUTTON_U union;
    public byte fsState { get { return union.fsState; } set { union.fsState = value; } }
    public byte fsStyle { get { return union.fsStyle; } set { union.fsStyle = value; } }
    public UIntPtr dwData;
    public IntPtr iString;
}

Marshal.SizeOf returns 32 on x64 processes and 20 on x86 processes, and everything ends up where it should when I pass this to SendMessage. I knew you could do it, C#!

Answer 2

Your best bet is to define two versions, one for 32 bit and one for 64 bit.

public struct TBBUTTON32
{
    int       iBitmap;
    int       idCommand;
    byte      fsState;
    byte      fsStyle;
    [MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 2)]
    byte[]    bReserved;
    UIntPtr   dwData;
    IntPtr    iString;
}

The 64 bit version is just the same but with SizeConst = 6 on the reserved bytes array.

Then you need to switch between them at runtime. Your C# code will have to detect whether it's running as a 32 or 64 bit process.