C++ Struct in C#

问题

I'm using a DLL written in C++ in my C# project by using DllImport and one of the functions I'm using looks like this:

    [DllImport("dds.dll", CharSet = CharSet.Auto)]
    private static extern int Par(
        ddTableResults2 tableResult,
        ref parResults ParResult,
        int vul
    );

The parResults struct is defined in C++ like this:

struct parResults {
  /* index = 0 is NS view and index = 1 
     is EW view. By 'view' is here meant 
     which side that starts the bidding. */
  char          parScore[2][16];
  char          parContractsString[2][128]; 
};

The start of the C++ function

int STDCALL Par(struct ddTableResults * tablep, struct parResults *presp, 
    int vulnerable)

How should I define the above struct in C# to able to send that struct as en reference into the DLL function?

This is what I have tried but don't work at all and I just get a Access Violation Error

    [StructLayout(LayoutKind.Sequential)]
    public struct parResults
    {
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
        public char[,] parScore;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
        public char[,] parContractsString;

        public parResults(int x)
        {
            parScore = new char[2,16];
            parContractsString = new char[2,128];
        }
    }

回答1:

This is quite a tricky struct to marshal in C#. There are various ways to attempt it, but I think that it will be cleanest to represent the character arrays as byte arrays and marshal to and from strings by hand. Here is a demonstration of what I mean:

C++

#include <cstring>

struct parResults {
    char          parScore[2][16];
    char          parContractsString[2][128];
};

extern "C"
{
    __declspec(dllexport) void foo(struct parResults *res)
    {
        strcpy(res->parScore[0], res->parContractsString[0]);
        strcpy(res->parScore[1], res->parContractsString[1]);
    }
}

C#

using System;
using System.Text;
using System.Runtime.InteropServices;

namespace ConsoleApplication1
{
    class Program
    {
        [StructLayout(LayoutKind.Sequential)]
        class parResults 
        {
            private const int parScoreCount = 2;
            private const int parScoreLen = 16;
            private const int parContractsStringCount = 2;
            private const int parContractsStringLen = 128;

            [MarshalAs(UnmanagedType.ByValArray, 
                SizeConst = parScoreCount * parScoreLen)]
            private byte[] parScoreBuff;

            [MarshalAs(UnmanagedType.ByValArray, 
                SizeConst = parContractsStringCount * parContractsStringLen)]
            private byte[] parContractsStringBuff;

            public string getParScore(int index)
            {
                string str = Encoding.Default.GetString(parScoreBuff, 
                    index * parScoreLen, parScoreLen);
                int len = str.IndexOf('\0');
                if (len != -1)
                    str = str.Substring(0, len);
                return str;
            }

            public void setParScore(int index, string value)
            {
                byte[] bytes = Encoding.Default.GetBytes(value);
                int len = Math.Min(bytes.Length, parScoreLen);
                Array.Copy(bytes, 0, parScoreBuff, index * parScoreLen, len);
                Array.Clear(parScoreBuff, index * parScoreLen + len,
                    parScoreLen - len);
            }

            public string parContractsString(int index)
            {
                string str = Encoding.Default.GetString(parContractsStringBuff,
                    index * parContractsStringLen, parContractsStringLen);
                int len = str.IndexOf('\0');
                if (len != -1)
                    str = str.Substring(0, len);
                return str;
            }

            public void setParContractsString(int index, string value)
            {
                byte[] bytes = Encoding.Default.GetBytes(value);
                int len = Math.Min(bytes.Length, parContractsStringLen);
                Array.Copy(bytes, 0, parContractsStringBuff,
                    index * parContractsStringLen, len);
                Array.Clear(parContractsStringBuff, 
                    index * parContractsStringLen + len,
                    parContractsStringLen - len);
            }

            public parResults()
            {
                parScoreBuff = new byte[parScoreCount * parScoreLen];
                parContractsStringBuff = 
                    new byte[parContractsStringCount * parContractsStringLen];
            }
        };

        [DllImport(@"...", CallingConvention = CallingConvention.Cdecl)]
        static extern void foo([In,Out] parResults res);

        static void Main(string[] args)
        {
            parResults res = new parResults();
            res.setParContractsString(0, "foo");
            res.setParContractsString(1, "bar");
            foo(res);
            Console.WriteLine(res.getParScore(0));
            Console.WriteLine(res.getParScore(1));
            Console.ReadLine();
        }
    }
}

---

Here I've used a class to represent the struct. Since a class in C# is a reference, we don't declare the parameters of that type with ref. I've also used __cdecl for convenience to avoid having to work out what the decorated name of the function would be. But your library used __stdcall and so you need to stick to that.

The class demonstrates sending data in both directions. You could probably simplify the code if the data flow was more restricted.

来源：https://stackoverflow.com/questions/26510206/c-struct-in-c-sharp