问sockaddr_in不支持地址族

EN

sock = socket (AF_INET, SOCK_DGRAM, 0) ;    
memset (&serv_addr, 0, sizeof (serv_addr)) ;
serv_addr.sin_family = AF_INET ;
serv_addr.sin_port   = htons (atoi(argv[1])) ;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY) ;

ret = bind(sock, (struct sockaddr *)&serv_addr, sizeof (serv_addr)) ;
// ...
ret = recvfrom (sock, buff, BUFF_SIZE, 0, (struct sockaddr *)&cli_addr, &addr_len ) ;
if (ret < 0)
{
    perror ("recvfrom\n") ;
    exit (EXIT_FAILURE) ;
}

printf ("%d received :\n\t%s\n", ret, buff) ;
printf ("Sending: \n\t%s\n", buff) ;

addr_len = sizeof (cli_addr) ;
ret = sendto (
    sock,
    buff,
    BUFF_SIZE,
    0,
    (struct sockaddr *)&cli_addr,
    addr_len
) ;
if (ret < 0)
{
    perror ("sendto\n") ;
    exit (EXIT_FAILURE) ;
}

printf ("%d char sent\n", ret) ;
close (sock) ;