使用RtlMoveMemory将VB6转换为C＃

Question

I am attempting to convert an existing VB6 application to C#. The application must use an API that was also written in VB6 and is an ActiveX DLL. I am using the .NET Interop functionality to wrap this API so that I can use it in C#.

The problem is a bit of code that gets a byte array, and then uses RtlMoveMemory() to move it into a Struct. With the C# code given below, I get a System.ArgumentException "Value does not fall within the expected range" exception. I have tried various permutations of this implementation, as well as some Marshalling, but I am a bit out of my depth in this area. Everything I tried resulted in some form of unhandled exception.

A solution using RtlMoveMemory() would be fine, but a solution using Marshalling would be even better. Hopefully it's just a matter of connecting the dots.

VB6 Code:

Public Declare Sub MoveIt Lib "kernel32.dll" Alias "RtlMoveMemory" (dest As Any, src As Any, ByVal bytes As Long)

Type IntEventStruct
    TTag As Double
    quality As Long
    Value As Single
End Type


Dim byteBuff(PACKETSIZE - 1) As Byte
Dim dEvent As IntEventStruct


Call DWApi.ReadEvent(code, DBIndex, TTStr, interval, byteBuff, errMsg)
Call MoveIt(dEvent, byteBuff(0), Len(dEvent))

C# Code:

[DllImport("kernel32.dll", EntryPoint="RtlMoveMemory")]
static extern void MoveIt(Object Destination, Object Source, long Length);

public struct ReadEventStruct
{
    public double TimeTag;
    public int Quality;
    public float Value;
}

byte[] byteBuff = new byte[BUFFER_SIZE];
ReadEventStruct dwRead = new ReadEventStruct();

this.dw.ReadEvent(pt.Plant, pt.Index, pt.Time, pt.Interval, ref byteBuff, ref errMsg);
MoveIt(dwRead, byteBuff, Marshal.SizeOf(dwRead));

The relevant API documentation for ReadEvent() (I don't have access to the source code):

This routine retrieves process data for a specified point at a single time.
Calling convention:

Call DWPCAPI.ReadEvent(Plant As String, _
  iChannel As Long, _
  StartT As String, _
  Interval as Single, _
  Buffer() As Byte, _
  ErrMsg As String)

Buffer( ):  Byte buffer containing returned data.

Answer 1

You can use fixed memory with a pinned pointer (remember that C# uses managed memory, so the system is free to move your objects around in memory).

Use:

[DllImport("Kernel32.dll", EntryPoint = "RtlMoveMemory")]
private static unsafe extern void MoveMemory(void* dest, void* src, int size);

and in your method, something like:

fixed (byte* p = pointer )
{
    // RtlMoveMemory call
}

The Other way is to use Marshal.PtrToStructure() .

Answer 2

The best answer was provided in a comment on my original question. It suggests using the BitConverter class instead of marshalling, but since the commenter didn't provide it as an answer, here it is:

ReadEventStruct dwRead = new ReadEventStruct(); 
Array buffer = new byte[BUFFER_SIZE];

this.dw.ReadEvent(pt.Plant, pt.Index, pt.Time, pt.Interval, ref buffer, ref errMsg);

byte[] byteBuffer = (byte[])buffer;                         // Convert to byte[] so BitConverter class can be used

dwRead.TimeTag = BitConverter.ToDouble(byteBuffer, 0);      // First 8 bytes are TimeTag (double)
dwRead.Quality = BitConverter.ToInt32(byteBuffer, 8);       // Next 4 bytes are Quality (integer)
dwRead.Value   = BitConverter.ToSingle(byteBuffer, 12);     // Last 4 bytes are Value (float)