Question

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Marshal C++ struct array into C#

I have an C++ .dll and I must use it with C# but there are some problems. First of all this is one of them.

Here for using C++ .dll file I must rechange below C++ struct to C# struct. Help me pls.

C++ sturcture:

typedef struct USMC_Devices_st{
      DWORD NOD;             // Number of the devices ready to work

      char **Serial;        // Array of 16 byte ASCII strings
      char **Version;       // Array of 4 byte ASCII strings
} USMC_Devices;

Answer 1

struct USMC_DEVICES_st would translate to something akin to:

using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
    struct USMC_DEVICES_st
    {
        public UInt32 NOD;

        public IntPtr serial;

        public IntPtr Version;
    }

Accessing Serial and Version could be done with code such as:

IntPtr ser;

for (var i = 0;
     (ser = Marshal.ReadIntPtr(um.serial, i)) != IntPtr.Zero;
     i += Marshal.SizeOf(ser))
{
    var serial = Marshal.PtrToStringAnsi(ser);
}

Edit – Following your comments here is a more detailed example of accessing the struct’s members:

static void PrintDevices(USMC_DEVICES_st um)
        {
            const int serialSize = 16;
            const int verSize = 4;
            int j = 0;
            for (var i= 0; i < um.NOD; i++, j+= IntPtr.Size)
            {
                var ser = Marshal.ReadIntPtr(um.serial, j);
                var ver = Marshal.ReadIntPtr(um.Version, j);
                // ensure we check for null pointers - just in case
                if (ver == IntPtr.Zero || ser == IntPtr.Zero) break;

                Console.WriteLine("Device {0}, \tSerial number {1}",
                                    Marshal.PtrToStringAnsi(ser, serialSize),
                                    Marshal.PtrToStringAnsi(ver, verSize));
            }
        }