下面的C#代码定义了一个函数用于判断指定的端口是否已经被占用。
代码转自： http://www.cnblogs.com/smiler/

public static bool PortInUse(int port)  {      bool inUse = false;                     IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties();      IPEndPoint[] ipEndPoints = ipProperties.GetActiveTcpListeners();                     foreach (IPEndPoint endPoint in ipEndPoints)      {          if (endPoint.Port == port)          {              inUse = true;              break;          }      }         return inUse;  }

下面的范例代码占用了8080端口，然后用上面定义的函数检测端口是否被占用

static void Main(string[] args)  {      HttpListener httpListner = new HttpListener();      httpListner.Prefixes.Add("http://*:8080/");      httpListner.Start();         Console.WriteLine("Port: 8080 status: " + (PortInUse(8080) ? "in use" : "not in use"));         Console.ReadKey();         httpListner.Close();  }