Struct parameter c# to c++

Question

I want to call a function from a c++ dll that accepts a struct as parameter in my c# code.

#include <iostream>

#include <cstring>

#define _e extern "C" __declspec(dllexport)

#define _i extern "C" __declspec(dllimport)



struct Args {

  std::string ip;

  std::string uparams;

};

_e std::string PAGE(Args args)

{

    std::string arguments = args.uparams;

    std::string buffer = "Hello World!!! <<--->> arguments -> \"";

    buffer += arguments;

    buffer += "\"";

    return buffer;

}

C# code

         [DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]

        static extern int LoadLibrary(

            [MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);



        [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]

        static extern IntPtr GetProcAddress(int hModule,

            [MarshalAs(UnmanagedType.LPStr)] string lpProcName);



        [DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]

        static extern bool FreeLibrary(int hModule);



        struct Arguments

        {

            public string ip;

            public string uparams;

        };

        delegate string Str([MarshalAs(UnmanagedType.Struct)] Arguments args);

        static void Main(string[] args)

        {

            int a = LoadLibrary("C:\\CTEST.dll");

            if (a < 1) {

                Console.Write("Cannot load library");

                Console.Read();

                return;

            }

            Console.WriteLine("Library Loaded");

            Console.Read();

            Str st = (Str)Marshal.GetDelegateForFunctionPointer(GetProcAddress(a, "PAGE"), typeof(Str));

            Arguments ar;

            ar.ip = "127.0.0.1";

            ar.uparams = "Hell Yeah";

            Console.WriteLine(st(ar));

            FreeLibrary(a);

        }

But i get the folowing error when i call st() function 

Attempted to read or write protected memory. This is often an indication that other memory is corrupt

L.E Sorry for the bad section of my other thread.