关于shutdown函数

shutdown 函数

close有两个限制可由函数shutdown来避免:

close将描述字的访问计数减1，仅在此计数为0时才关闭套接口
shutdown可激发TCP的正常连接终止序列, 而不管访问计数。

close终止了数据传送的两个方向：读和写。
shutdown终止的数据传送的两个方向：读和写, 或其中任一方向：读或写

定义：
int shutdown( int sockfd, int howto) ;

howto选项:
SHUT_RD 关闭连接的读一半
SHUT_WR 关闭连接的写这一半
SHUT_RDWR 关闭连接读读和写

/* -*-C-*- tcpprobe.c */
/* tcpprobe - report on which tcp ports accept connections */
/* IO ERROR, [e-mail], Sep 15, 1995 */

#include
#include
#include
#include
#include
#include

int main(int argc, char **argv)
{
  int probeport = 0;
  struct hostent *host;
  int err, i, net;
  struct sockaddr_in sa;

  if (argc != 2) {
    printf("Usage: %s hostname\n", argv[0]);
    exit(1);
  }

  for (i = 1; i < 1024; i++) {
    strncpy((char *)&sa, "", sizeof sa);
    sa.sin_family = AF_INET;
    if (isdigit(*argv[1]))
      sa.sin_addr.s_addr = inet_addr(argv[1]);
    else if ((host = gethostbyname(argv[1])) != 0)
      strncpy((char *)&sa.sin_addr, (char *)host->h_addr, sizeof sa.sin_addr);
    else {
      herror(argv[1]);
      exit(2);
    }
    sa.sin_port = htons(i);
    net = socket(AF_INET, SOCK_STREAM, 0);
    if (net < 0) {
      perror("\nsocket");
      exit(2);
    }
    err = connect(net, (struct sockaddr *) &sa, sizeof sa);
    if (err < 0) {
      printf("%s %-5d %s\r", argv[1], i, strerror(errno));
      fflush(stdout);
    } else {
      printf("%s %-5d accepted.                               \n", argv[1], i);
      if (shutdown(net, 2) < 0) {
        perror("\nshutdown");
        exit(2);
      }
    }
    close(net);
  }
  printf("                                                                \r");
  fflush(stdout);
  return (0);
}