网络示意图

不同于前面的TCP UDP 没有连接的概念 所以绑定以后不用侦听 直接收发就行
所以只需要开启一个服务器socket 就是 不需要对应的每个数据传输的socket

Socket_UDP 服务端逻辑

1 设置地址和选择协议IPV4/IPV6

 struct sockaddr_in addr;
  addr.sin_family     = AF_INET;
  addr.sin_port       = htons(9876);
  addr.sin_addr.s_addr = htonl(INADDR_ANY);

2 初始好客户端的socket_in

  struct sockaddr_in clientAddr;
  int n;
  int len = sizeof(clientAddr);

3 创建和绑定socket

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
  {
    
    
      printf("socket error.\n");
      exit(1);
  }

  if (bind(sock, (struct sockaddr *) &addr, sizeof(addr)) < 0)
  {
    
    
    printf("bind error.\n");
    exit(1);
  }

4 收发数据

  while (1)
  {
    
    
    n = recvfrom(sock, buff_recv, 511, 0, (struct sockaddr *) &clientAddr, &len);
    if (n > 0)
    {
    
    
      buff_recv[n] = 0;
      printf("recv data from client:%s %u says: %s\n", inet_ntoa(clientAddr.sin_addr), ntohs(clientAddr.sin_port), buff_recv);
      n = sendto(sock, buff_send, n, 0, (struct sockaddr *) &clientAddr, sizeof(clientAddr));
      if (n < 0)
      {
    
    
        printf("sendto error.\n");
        break;
      }else {
    
    
        printf("recv error.\n");
        break;
      }
    }
    return 0;
  }

Socket_UDP 客户端逻辑

和TCP 相比少了connect 的概念

1 初始化各项操作 1目标地址 2buffer

    struct sockaddr_in addr;
    int sock;

    addr.sin_family     = AF_INET;
    addr.sin_port       = htons(9876);
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");

2 初始化Socket

 if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
    
    
      printf("socket error.\n");
      exit(1);
    }

    if (addr.sin_addr.s_addr == INADDR_NONE)
    {
    
    
      printf("Incorrect ip address!");
      close(sock);
      exit(1);
    }

3 收发消息

    n = sendto(sock, buff_send, strlen(buff_send), 0, (struct sockaddr *) &addr, sizeof(addr));
    if (n < 0)
    {
    
    
      printf("sendto error.\n");
      close(sock);
    }

    n = recvfrom(sock, buff_recv, 512, 0, (struct sockaddr *) &addr, &len);
    if (n > 0)
    {
    
    
        buff_recv[n] = 0;
        printf("received from sever:");
        puts(buff_recv);
    }