(精华)2020年9月10日 C#基础知识点 调用动态链接库DLL(调用系统Api和其他语言编写的DLL)

public partial class Program { static void FileMethod() { //var fs = new FileOpen("d:\\data.txt");//自定义调用 var fs = File.Open("data.txt", FileMode.OpenOrCreate);//系统调用 var bytes = new byte[fs.Length]; var count = (int)fs.Length; var offset = 0; while (count > 0) { var n = fs.Read(bytes, offset, count); if (n == 0) break; offset += n; count -= n; } } } public class FileOpen { public const uint GENERIC_READ = 0x80000000; public const uint GENERIC_WRITE = 0x40000000; public const uint CREATE_NEW = 1; public const uint CREATE_ALWAYS = 2; public const uint OPEN_EXISTING = 3; // 使用interop调用CreateFile函数有关CreateFile的详细信息请参阅非托管MSDN参考库 // DllImport调用动态链接库自动寻找windowsAPI kernel32.dll库包含内存管理等 [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)] static extern SafeFileHandle CreateFile(string lpFileName, uint dwDesiredAccess, uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition, uint dwFlagsAndAttributes, IntPtr hTemplateFile); private SafeFileHandle _handleValue; public FileOpen(string path) { Load(path); } public void Load(string path) { if (string.IsNullOrEmpty(path)) { throw new ArgumentNullException(nameof(path)); } _handleValue = CreateFile(path, GENERIC_WRITE, 0, IntPtr.Zero, CREATE_ALWAYS, 0, IntPtr.Zero); if (_handleValue.IsInvalid) { Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error()); } } }