linux udp c/s

一、UDP C/S编程的步骤如下图所示

二、与TCP C/S通信的区别在于：
服务端没有设置监听和等待连接的过程。客户端没有连接服务端的过程。
基于UDP的通信时不可靠地，面向无连接的，发送的数据无法确切知道对方收到没有，就算对方根本不存在，也可以发送数据出去。
这样的通信通常用在对可靠性、安全性要求不高的地方，比如语音通信（没听清楚可以让对方再说一遍）。

三、server端编程

 #include <sys/types.h>
 #include <sys/socket.h>
 #include<pthread.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
 #include <stdlib.h>

 int main(int argc, char **argv)
 {
     if (argc != )
     {
         printf("Usage: %s port\n", argv[]);
         exit();
     }
     printf("Welcome! This is a UDP server, I can only received message from client and reply with same message\n");

     struct sockaddr_in addr;   
     addr.sin_family = AF_INET;
     addr.sin_port = htons(atoi(argv[]));    //协商的发送端的端口号
     addr.sin_addr.s_addr = htonl(INADDR_ANY); //本机地址

     int sock;
     if ( (sock = socket(AF_INET, SOCK_DGRAM, )) < )
     {
         perror("socket");
         exit();
     }
     if (bind(sock, (struct sockaddr *)&addr, sizeof(addr)) < ) //绑定socket套接字到本地的监听端口
     {
         perror("bind");
         exit();
     }
     char buff[];
     struct sockaddr_in clientAddr;
     int n;
     int len = sizeof(clientAddr);
     while ()
     {
         n = recvfrom(sock, buff, , , (struct sockaddr*)&clientAddr, &len);//接收UDP包
         if (n>)
         {
             buff[n] = ;
             printf("%s %u says: %s\n", inet_ntoa(clientAddr.sin_addr), ntohs(clientAddr.sin_port), buff);
             n = sendto(sock, buff, n, , (struct sockaddr *)&clientAddr, sizeof(clientAddr));//往发送方发送UDP回复包
             if (n < )
             {
                 perror("sendto");
                 break;
             }
         }
         else
         {
             perror("recv");
             break;
         }
     }
     return ;
 }

四、client端

 #include <sys/types.h>
 #include <sys/socket.h>
 #include<pthread.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
 #include <stdlib.h>

 int main(int argc, char **argv)
 {
     if (argc != )
     {
         printf("Usage: %s ip port", argv[]);
         exit();
     }
     printf("This is a UDP client\n");
     struct sockaddr_in addr;
     int sock;

     if ( (sock=socket(AF_INET, SOCK_DGRAM, )) <)//创建socket
     {
         perror("socket");
         exit();
     }
     addr.sin_family = AF_INET;
     addr.sin_port = htons(atoi(argv[]));
     addr.sin_addr.s_addr = inet_addr(argv[]);//对方的IP地址、端口号
     if (addr.sin_addr.s_addr == INADDR_NONE)
     {
         printf("Incorrect ip address!");
         close(sock);
         exit();
     }

     char buff[];
     int len = sizeof(addr);
     while ()
     {
         gets(buff);
         int n;
         n = sendto(sock, buff, strlen(buff), , (struct sockaddr *)&addr, sizeof(addr));//往对方地址发送UDP包
         if (n < )
         {
             perror("sendto");
             close(sock);
             break;
         }
         n = recvfrom(sock, buff, , , (struct sockaddr *)&addr, &len);//接收来自对方IP地址的UDP包
         if (n>)
         {
             buff[n] = ;
             printf("received:");
             puts(buff);
         }
         else if (n==)
         {
             printf("server closed\n");
             close(sock);
             break;
         }
         else if (n == -)
         {
             perror("recvfrom");
             close(sock);
             break;
         }
     }

     return ;
 }

转自：http://www.cnblogs.com/uvsjoh/archive/2013/01/01/2841764.html