C#的互操作性：缓冲区、结构、指针

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 = 2)]
public char[] rgchMember;
}
static void Main(string[] args)
{
MyBeep(500, 500);
//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(255);
GetCurrentDirectory(255, 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);
}
}
}