How to do CreateFileMapping in a C++ DLL and access it in C#, VB and C++

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        [DllImport("sharedmem.dll")]
        extern static int GetRecordCount();

        [DllImport("sharedmem.dll")]
        extern static void SetValue(
            [MarshalAs(UnmanagedType.LPTStr)] string key,
            [MarshalAs(UnmanagedType.LPTStr)] string value);

        [DllImport("sharedmem.dll")]
        extern static IntPtr GetValue([MarshalAs(UnmanagedType.LPTStr)]string key);

        public Form1()
        {
            InitializeComponent();
        }

        private void UpdateRecordCount(object sender, EventArgs e)
        {
            linkLabel2.Text = "Count = " + GetRecordCount().ToString();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //Set
            SetValue(textBox1.Text, textBox2.Text);
            UpdateRecordCount(null, null);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            StringBuilder sb = new StringBuilder();
            IntPtr intPtr = GetValue(textBox1.Text);
            textBox2.Text = Marshal.PtrToStringUni(intPtr);
            UpdateRecordCount(null, null);
        }


    }
}