Managed C++/CLI

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.ComponentModel;

namespace GryphonSoft.Utility.Runtime.InteropServices
{
    /// <summary>
    /// Helper class to manipulate the DLL Search Path.
    /// </summary>
    public static class DllSearchPath
    {

        #region Fields

        private static Dictionary<string, IntPtr> _dllPathCookieDict;

        private static SetDefaultDllDirectories_Delegate _SetDefaultDllDirectories;
        private static AddDllDirectory_Delegate _AddDllDirectory;
        private static RemoveDllDirectory_Delegate _RemoveDllDirectory;

        #endregion

        #region Constructor

        static DllSearchPath()
        {
            _dllPathCookieDict = new Dictionary<string, IntPtr>(StringComparer.OrdinalIgnoreCase);

            IntPtr kernel32 = LoadLibrary("Kernel32.dll");

            _SetDefaultDllDirectories = Marshal.GetDelegateForFunctionPointer<SetDefaultDllDirectories_Delegate>(GetProcAddress(kernel32, "SetDefaultDllDirectories"));
            _AddDllDirectory = Marshal.GetDelegateForFunctionPointer<AddDllDirectory_Delegate>(GetProcAddress(kernel32, "AddDllDirectory"));
            _RemoveDllDirectory = Marshal.GetDelegateForFunctionPointer<RemoveDllDirectory_Delegate>(NativeMethods.GetProcAddress(kernel32, "RemoveDllDirectory"));

            _SetDefaultDllDirectories(0x00001000); /* 0x00001000 == LOAD_LIBRARY_SEARCH_DEFAULT_DIRS */

        }

        #endregion
        
        #region Delegates

        private delegate bool SetDefaultDllDirectories_Delegate(int DirectoryFlags);
        private delegate IntPtr AddDllDirectory_Delegate(string NewDirectory);
        private delegate bool RemoveDllDirectory_Delegate(IntPtr Cookie);

        #endregion

        #region P/Invoke

        [DllImport("Kernel32.dll")]
        internal static extern IntPtr LoadLibrary(string lpFileName);

        [DllImport("Kernel32.dll")]
        internal static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);

        #endregion

        #region Public API

        /// <summary>
        /// Adds a directory from the DLL Search Path.
        /// </summary>
        /// <param name="dir">The directory to add.</param>
        /// <exception cref="Win32Exception">If an error occurred while adding the directory.</exception>
        public static void AddDllDirectory(string dir)
        {
            IntPtr cookie = _AddDllDirectory(dir);

            if (cookie == IntPtr.Zero) throw new Win32Exception();

            _dllPathCookieDict.Add(dir, cookie);

        }

        /// <summary>
        /// Removes a previously added directory from the DLL Search Path.
        /// </summary>
        /// <param name="dir">The directory to remove.</param>
        /// <returns><see langword="true"/> if the directory was removed, <see langword="false"/> otherwise.</returns>
        /// <exception cref="Win32Exception">If an error occurred while removing the directory.</exception>
        public static bool RemoveDllDirectory(string dir)
        {
            IntPtr cookie;
            if(!_dllPathCookieDict.TryGetValue(dir, out cookie))
            {
                return false;
            }
            if (!_RemoveDllDirectory(cookie)) throw new Win32Exception();
            _dllPathCookieDict.Remove(dir);
            return true;
        }

        #endregion

    }
}