如何将 C++ struct 数组编组为 C#

Question

I plan to marshall a c++ struct array into c# and I tried a lot of methods to do it but the array that the function returns is an empty array all the time. I don't know what the problem is. Here is my c++ code:

# include<iostream>
typedef  struct
{
    float x, y, z;
}cfloat3;

extern "C" __declspec(dllexport)  cfloat3* Test();
extern "C" __declspec(dllexport)  void freeMemory(cfloat3 * a);

cfloat3* Test()
{
    cfloat3* a = new cfloat3[5];
    for (int i = 0; i < 5; i++)
    {
        a[i].x = 1;
        a[i].y = 1;
        a[i].z = 1;
    }
    return a;
}
void freeMemory(cfloat3* a)
{
    delete[] a;
}

and here is my c# code

namespace ConsoleApp3
{
    [StructLayout(LayoutKind.Sequential)]
    struct cfloat3
    {
        public float x, y, z;
    }
    class Program
    {
        [DllImport("Dll1.dll", EntryPoint = "Test")]
        public static extern IntPtr Test();

        [DllImport("Dll1.dll", EntryPoint = "freeMemory")]
        public static extern void freeMemory( IntPtr a);
        static void Main(string[] args)
        {

            int length = 5;
            int size = Marshal.SizeOf(typeof(cfloat3)) * length;

            IntPtr pBuff = Marshal.AllocHGlobal(size);
            cfloat3[] pClass = new cfloat3[length];
            pBuff=Test();

            IntPtr[] bb = new IntPtr[length];
            Marshal.Copy(pBuff, bb, 0, length);

            for (int i = 0; i < length; i++)
            {
                pClass[i] = (cfloat3)Marshal.PtrToStructure(bb[i],typeof(cfloat3));

                Console.WriteLine(pClass[i].x);
                Console.WriteLine(pClass[i].y);
                Console.WriteLine(pClass[i].z);

            }
            Marshal.FreeHGlobal(pBuff);
            Console.ReadKey();
        }
    }
}

Run this program, I get "System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

Answer 1

You need to use MarshalAs annotation with SizeConst in each field and return type of the C# individually mapped to c++ struct and return type

Please refer this answer Marshaling C++ struct to C#