Sharing Memory Mapped File Structure between c++ and c#

Question

I have 2 applications, 1 is C++ and one is C# made. The following is my structure inside C++:

struct INFO
{
    char Name[MAX_PATH];
    int Number;
};

The following is my attempt to replicate the structure in C#:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct INFO
{
   public byte Name;
   public int Number;
}

The C++ Program ( ready to compile and test ):

#include <stdio.h>
#include <tchar.h>
#include <iostream>
using namespace std;

#define WIN32_LEAN_AND_MEAN
#define _WIN32_WINNT _WIN32_WINNT_WINXP

// System Include
#include <windows.h>
#include <winsock2.h>

struct INFO
{
    char Name[MAX_PATH];
    int Number;
};

HANDLE FileMappingHandle;
INFO* FileMapping;

void EntryProc()
{
    if ((FileMappingHandle = CreateFileMapping(INVALID_HANDLE_VALUE, 0, PAGE_READWRITE, 0, sizeof(INFO), "Local\\INFO_MAPPING")) == 0)
    {
        return;
    }

    if ((FileMapping = (INFO*)MapViewOfFile(FileMappingHandle, FILE_MAP_ALL_ACCESS, 0, 0, sizeof(INFO))) == 0)
    {
        return;
    }

    strcpy(FileMapping->Name, "DARKVADER");

    FileMapping->Number = 1337;

    printf("FileMapping->Name: %s", FileMapping->Name);
    printf("FileMapping->Number: %d", FileMapping->Number);
}


int main()
{
    EntryProc();
    do {
        cout << '\n' << "Press the Enter key to continue.";
    } while (cin.get() != '\n');
    return 0;
}

The C# Program ( ready to compile and test ):

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.IO.MemoryMappedFiles;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {

            InitializeComponent();
            this.DoMap();
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public struct INFO
        {
            public byte Name;
            public int Number;
        }

        public void DoMap()
        {
            MemoryMappedFileSecurity CustomSecurity = new MemoryMappedFileSecurity();
            CustomSecurity.AddAccessRule(new System.Security.AccessControl.AccessRule<MemoryMappedFileRights>("everyone", MemoryMappedFileRights.FullControl, System.Security.AccessControl.AccessControlType.Allow));

            //access memory mapped file (need persistence)
            using (var memMapFile = MemoryMappedFile.CreateOrOpen("Local\\INFO_MAPPING", 1024, MemoryMappedFileAccess.ReadWriteExecute, MemoryMappedFileOptions.None, CustomSecurity, System.IO.HandleInheritability.Inheritable))
            {
                using (var accessor = memMapFile.CreateViewAccessor())
                {
                    INFO data;

                    accessor.Read<INFO>(0, out data);

                    Console.WriteLine(data.Name);
                    Console.WriteLine(data.Number);
                }
            }
        }

    }
}

The Problem:

I can share numbers between the two applications using the above code, but I cannot share strings.

When I say "cannot" share, what I actually means is that instead of the actual "characters" I always get wierd chinese symbols, and even the number dissapears.

I have tried all the combinations I could think of ( byte[], string, unsafe struct, etc), in the C# struct but I have failed.

Please show me / explain to me how can I share properly strings between my 2 applications.

Example working code would be appreciated.

Answer 1

To share strings you need to map them properly: https://docs.microsoft.com/en-us/dotnet/framework/interop/default-marshaling-for-strings

Probably, you need to decorate ( ByValTStr uses CharSet from your StructLayout , so it's ANSI):

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = MAX_PATH)]
string Name;

EDIT: Checked on .net core. It's not allowed to use reference types in Accessor. The easiest option would be reading the array and extracting values.

var buffer = new byte[264];
accessor.ReadArray(0, buffer, 0, buffer.Length);
var endIndex = Array.FindIndex(buffer, 0, 260, x => x == 0);
var name = Encoding.ASCII.GetString(buffer, 0, endIndex == -1 ? 260 : endIndex);
var number = BitConverter.ToInt32(buffer, 260);

Another one is using unsafe:

[StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
public unsafe struct INFO
{
    [FieldOffset(0)]
    public fixed byte Name[260];
    [FieldOffset(260)]
    public int Number;
}

class Program
{
    static void Main(string[] args)
    {
        //CustomSecurity.AddAccessRule(new System.Security.AccessControl.AccessRule<MemoryMappedFileRights>("everyone", MemoryMappedFileRights.FullControl, System.Security.AccessControl.AccessControlType.Allow));

        //access memory mapped file (need persistence)
        using (var memMapFile = MemoryMappedFile.CreateOrOpen(
            "Local\\INFO_MAPPING",
            1024,
            MemoryMappedFileAccess.ReadWriteExecute,
            MemoryMappedFileOptions.None,
            System.IO.HandleInheritability.Inheritable))
        {
            using (var accessor = memMapFile.CreateViewAccessor())
            {
                accessor.Read<INFO>(0, out INFO data);
                string name;
                unsafe
                {
                    name = new String((sbyte*)data.Name, 0, 260);
                }
                Console.WriteLine(name);
                Console.WriteLine(data.Number);
            }
        }
    }