netcat源代码分析，doconnect()函数的作用

在服务端是建立侦听套接字，参数中，最后一个不为0。

在客户端是直接和服务端连接，参数中，前两个参数第一个是服务端的ip地址，第二个是要连接的服务端的端口。

doconnect()

    fprintf(stderr,"in doconnect ,listen socket nnetfd = %d.\n",nnetfd);
  if (o_listen)
    return (nnetfd);            /* thanks, that's all for today */

dolisten()

    fprintf(stderr,"in dolisten lp = %d\n",lp);
/* Pass everything off to doconnect, who in o_listen mode just gets a socket */
  nnetfd = doconnect (rad, rp, lad, lp);

    fprintf(stderr,"in dolisten nnetfd = %d\n",nnetfd);

G:\nc\nc114-debug>nc -lp 66
in res_init
after recycle
after go: x now , optarg 0 optind 3
curport = (null)
in dolisten lp = 66
in doconnect
in doconnect ,listen socket nnetfd = 1864.
in dolisten nnetfd = 1864