WINSOCK_UDP

一、绪言

　　 UDP是一种面向非连接，不可靠的通讯协议，相对于TCP来说，虽然可靠性不及，但传输效率较高。所以在网络上仍有很大的用途。这几日需要了解下udp通讯的过程，上网发现这方面的资料还挺少。于是仔细的翻找了下msdn，基本上搞清楚了udp通讯的过程。做了一个测试的例子。希望对大家有帮助。

　　二、UDP的通讯过程

server端: open a socket(socket)--->name the socket(bind)--->send and receive data(sendto recvfrom)--->close socket(closesocket)
client端: open a socket(socket)---------------------------->send and receive data(sendto recvfrom)--->close socket(closesocket)

　　 server端无需listen，client端无需connect，因此udp中server和client的区别相对较模糊。只要调用sendto和recvfrom就可以给指定的地址收发数据，但并不保证收发的数据的完整性和可靠性。

　　三、示例

　　 udpserver主要代码：

#pragma comment(lib,"WSOCK32.lib")
#pragma comment(lib,"ws2_32.lib")
#include"stdio.h"
#include <Winsock2.h>

void main()
{

    WSADATA wsaData;
    int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if(iResult != NO_ERROR)
 {
        printf("Error at WSAStartup()\n");
  return;
 }

 SOCKET socket1;
 struct sockaddr_in local;
 struct sockaddr_in from;
 int fromlen =sizeof(from);
 local.sin_family=AF_INET;
 local.sin_port=htons(1000); ///监听端口
 local.sin_addr.s_addr=INADDR_ANY; ///本机
 
 socket1=socket(AF_INET,SOCK_DGRAM,0);
 bind(socket1,(struct sockaddr*)&local,sizeof local);
 while (1)
 {
  char buffer[1024]="/0";
  printf("waiting for message from others-------------/n");
  if (recvfrom(socket1,buffer,sizeof buffer,0,(struct sockaddr*)&from,&fromlen)!=SOCKET_ERROR)
  {
   printf("Received datagram from %s--%s/n",inet_ntoa(from.sin_addr),buffer);
   ////给cilent发信息
   sendto(socket1,buffer,sizeof buffer,0,(struct sockaddr*)&from,fromlen);
   
  }
  Sleep(500);
 }
 closesocket(socket1);
}

　　 udpcilent主要代码:

#pragma comment(lib,"WSOCK32.lib")
#pragma comment(lib,"ws2_32.lib")
#include"stdio.h"
#include <Winsock2.h>

void main()
{
 WSADATA wsaData;
    int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if(iResult != NO_ERROR)
 {
        printf("Error at WSAStartup()\n");
  return;
 }
 SOCKET socket1;
 struct sockaddr_in server;
 int len =sizeof(server);
 server.sin_family=AF_INET;
 server.sin_port=htons(1000); ///server的监听端口
 server.sin_addr.s_addr=inet_addr("168.168.1.112"); ///server的地址

 socket1=socket(AF_INET,SOCK_DGRAM,0);
 while (1)
 {
  char buffer[1024] = {0};
  printf("input message/n");
  //scanf("%s",buffer);
  if (strcmp(buffer,"bye")==0)
   break;
  if (sendto(socket1,buffer,sizeof buffer,0,(struct sockaddr*)&server,len)!=SOCKET_ERROR)
  {
   printf("++++++sendto success\n");
   //if (recvfrom(socket1,buffer,sizeof buffer,0,(struct sockaddr*)&server,&len) != SOCKET_ERROR)
   // printf("rece from server:%s/n",buffer);
  }
  else
  {
   printf("------sendto failed\n");
  }
  Sleep(500);
 }
 closesocket(socket1);
}