using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Runtime.InteropServices;

namespace Interop

{

    class Program

    {

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

        public static extern bool MyBeep(uint iFreq, uint iDuration);

        //HMODULE WINAPI LoadLibrary( _In_ LPCTSTR lpFileName);

        [DllImport("kernel32.dll")]

        public static extern IntPtr LoadLibrary(string dllName);

        delegate int deleMessageBox(IntPtr hWnd, string text, string caption, uint type);

        //GetProcAddress函数检索指定的动态链接库(DLL)中的输出库函数地址。

        //FARPROC GetProcAddress(

        //      HMODULE hModule, // DLL模块句柄

        //　　  LPCSTR lpProcName // 函数名

        //　　);

        [DllImport("kernel32.dll")]

        public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

        //CharSet = CharSet.Auto

        [DllImport("user32.dll", CharSet = CharSet.Auto)]

        public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type);

        //DWORD GetCurrentDirectory(DWORD nBufferLength, //sizeofdirectorybuffer

        //LPTSTR lpBuffer   //directorybuffer

        //);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]

        public static extern int GetCurrentDirectory(int BufferLength, System.Text.StringBuilder lpBuffer);

        //LPSTR GetCommandLine()

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]

        public static extern System.IntPtr GetCommandLine();

        //结构体

        //typedef struct{

        //    int wStructSize;

        //    int x;

        //    int y;

        //    int dx;

        //    int dy;

        //    int wMax;

        //    TCHAR rgchMember[2];

        //}HELPWININFO;

        [StructLayout(LayoutKind.Sequential)]

        public struct HELPWININFO

        {

            int wStructSize;

            int x;

            int y;

            int dx;

            int dy;

            int wMax;

            [MarshalAs(UnmanagedType.ByValArray, SizeConst = )]

            public char[] rgchMember;

        }

        static void Main(string[] args)

        {

            MyBeep(, );

            //函数需要修改内存缓冲区，必须用StringBuilder，因为String类型是只读的

            StringBuilder sb = new StringBuilder();

            GetCurrentDirectory(, sb);

            Console.WriteLine(sb);

            //使用IntPtr类将返回的字符串保存到string中

            IntPtr ptr = GetCommandLine();

            string cmdline = Marshal.PtrToStringAuto(ptr);

            Console.WriteLine(cmdline);

            //GetProcAddress

            IntPtr ptrKernel32 = LoadLibrary("user32.dll");

            IntPtr ptrProcMessageBox = GetProcAddress(ptrKernel32, "MessageBoxA");

            deleMessageBox messageBox = Marshal.GetDelegateForFunctionPointer(ptrProcMessageBox, typeof(deleMessageBox)) as deleMessageBox;

            messageBox(IntPtr.Zero, @"public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);", "LoadLibrary", 0x40);

            MessageBox(IntPtr.Zero, "Content Here!", "Caption", 0x40);

        }

    }

}