udp 网络编程服务端接收到的端口号与客户端中定义的端口号不一样，请高手指教。

[hei鹰]

为什么下面的程序在server端接收到的 端口号不是5150，而是2711，（或者其他的端口号，每次运行的结果都不一样）？？？
通过这句来打印：
printf("We successfully received %d bytes from address %s:%d.\n", Ret,
inet_ntoa(SenderAddr.sin_addr), ntohs(SenderAddr.sin_port));

server端：

#include <winsock2.h>
#include <stdio.h>

void main(void)
{
   WSADATA              wsaData;
   SOCKET               ReceivingSocket;
   SOCKADDR_IN          ReceiverAddr;
   int                  Port = 5150;
   char                 ReceiveBuf[1024];
   int                  BufLength = 1024;
   SOCKADDR_IN          SenderAddr;
   int                  SenderAddrSize = sizeof(SenderAddr);
   int                  Ret;


   // Initialize Winsock version 2.2

   if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
   {
      // NOTE: Since Winsock failed to load we cannot use WSAGetLastError 
      // to determine the error code as is normally done when a Winsock 
      // API fails. We have to report the return status of the function.

      printf("ERROR: WSAStartup failed with error %d\n", Ret);
      return;
   }

   
   // Create a new socket to receive datagrams on.
 
   if ((ReceivingSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))
       == INVALID_SOCKET)
   {
      printf("ERROR: socket failed with error %d\n", WSAGetLastError());
      WSACleanup();
      return;
   } 

   // Setup a SOCKADDR_IN structure that will tell bind that we
   // want to receive datagrams from all interfaces using port
   // 5150.

   ReceiverAddr.sin_family = AF_INET;
   ReceiverAddr.sin_port = htons(Port);    
   ReceiverAddr.sin_addr.s_addr = htonl(INADDR_ANY);

   // Associate the address information with the socket using bind.

   if (bind(ReceivingSocket, (SOCKADDR *)&ReceiverAddr, sizeof(ReceiverAddr))
       == SOCKET_ERROR)
   {
      printf("ERROR: bind failed with error %d\n", WSAGetLastError());
      closesocket(ReceivingSocket);
      WSACleanup();
      return;
   }

   printf("We are ready to receive 1 datagram from any interface on port %d...\n",
          Port);

   // At this point you can receive datagrams on your bound socket.

   if ((Ret = recvfrom(ReceivingSocket, ReceiveBuf, BufLength, 0,
       (SOCKADDR *)&SenderAddr, &SenderAddrSize)) == SOCKET_ERROR)
   {
      printf("ERROR: recvfrom failed with error %d\n", WSAGetLastError());
      closesocket(ReceivingSocket);
      WSACleanup();
      return;
   }

   printf("We successfully received %d bytes from address %s:%d.\n", Ret,
          inet_ntoa(SenderAddr.sin_addr), ntohs(SenderAddr.sin_port));


   // When your application is finished receiving datagrams close
   // the socket.

   closesocket(ReceivingSocket);

   // When your application is finished call WSACleanup.

   WSACleanup();
}





client端：
#include <winsock2.h>
#include <stdio.h>

void main(int argc, char **argv)
{
   WSADATA              wsaData;
   SOCKET               SendingSocket;
   SOCKADDR_IN          ReceiverAddr;
   int                  Port = 5150;
   int                  Ret;

   /*if (argc <= 1)
   {
      printf("USAGE: udpsender <receiver IP address>.\n");
      return;
   }*/

   // Initialize Winsock version 2.2

   if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
   {
      // NOTE: Since Winsock failed to load we cannot use WSAGetLastError 
      // to determine the error code as is normally done when a Winsock 
      // API fails. We have to report the return status of the function.

      printf("ERROR: WSAStartup failed with error %d\n", Ret);
      return;
   }
   
   // Create a new socket to receive datagrams on.
 
   if ((SendingSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))
       == INVALID_SOCKET)
   {
      printf("ERROR: socket failed with error %d\n", WSAGetLastError());
      WSACleanup();
      return;
   }

   // Setup a SOCKADDR_IN structure that will identify who we
   // will send datagrams to. For demonstration purposes, let's
   // assume our receiver's IP address is 136.149.3.29 and waits
   // for datagrams on port 5150. Obviously you will want to prompt 
   // the user for an IP address and port number and fill these 
   // fields in with the data from the user.

   ReceiverAddr.sin_family = AF_INET;
   ReceiverAddr.sin_port = htons(Port);    
   //ReceiverAddr.sin_addr.s_addr = inet_addr(argv[1]);
   ReceiverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
   // Send a datagram to the receiver.

   if ((Ret = sendto(SendingSocket, "Hello", 5, 0, 
       (SOCKADDR *)&ReceiverAddr, sizeof(ReceiverAddr))) == SOCKET_ERROR)
   {
      printf("ERROR: sendto failed with error %d\n", WSAGetLastError());
      closesocket(SendingSocket);
      WSACleanup();
      return;
   }

   // When your application is finished sending datagrams close
   // the socket.

   printf("We successfully sent %d byte(s) to %s:%d.\n", Ret,
          inet_ntoa(ReceiverAddr.sin_addr), htons(ReceiverAddr.sin_port));

   closesocket(SendingSocket);

   // When your application is finished call WSACleanup.

   WSACleanup();
}

[evahelen_study]

因为你的客户端没有调用bind，所以sendto时，系统选择一个临时端口，结果每次都不同，你可以看下《WinSock网络编程经络》，有介绍，这有很多socket例子： http://download.csdn.net/detail/geoff08zhang/4571358

[以免我忘记]

楼上正解。就是这样的。

[撑起头顶的天]

其实你就没理解服务端和客户端的连接 服务端的5150是说程序和计算机的5150端口绑定,所有到计算机5150的数据包,都会发到服务端 客户端的5150是说你要连接到服务端的5150端口.而不是说客户端必须从5150端口去连接服务器,其实你理解的前提是服务端和客户端是在两台不同的计算机上. 这样两者才能建立一条链接.

[hanyue03]

引用 3 楼 cqtddt 的回复:

其实你就没理解服务端和客户端的连接 服务端的5150是说程序和计算机的5150端口绑定,所有到计算机5150的数据包,都会发到服务端 客户端的5150是说你要连接到服务端的5150端口.而不是说客户端必须从5150端口去连接服务器,其实你理解的前提是服务端和客户端是在两台不同的计算机上. 这样两者才能建立一条链接.

正解

[Volatile_xian]

讲得真好