C、socket编程:使用select()将多个客户端连接到服务器 [英] C, socket programming: Connecting multiple clients to server using select()

问题描述

我正在尝试制作一个可以由多个客户端连接的服务器.到目前为止，这是我的代码:

I'm trying to make a server that can be connected to by multiple clients. Here's my code so far:

客户:

int main(int argc, char **argv) {

  struct sockaddr_in servaddr;
  int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

  if (sock == -1) perror("Socket");

  bzero((void *) &servaddr, sizeof(servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_port = htons(6782);
  servaddr.sin_addr.s_addr = inet_addr(<server_ip_address>);

  if (-1 == connect(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)))
    perror("Connect");

  while(1) {

    char message[6];
    fgets(message, 6, stdin);

    message[5] = '';

    send(sock, message, 6, 0);
  }


  close(sock);
}

服务器:

int main(int argc, char **argv) {

  fd_set fds, readfds;
  int i, clientaddrlen;
  int clientsock[2], rc, numsocks = 0, maxsocks = 2;

  int serversock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
  if (serversock == -1) perror("Socket");

  struct sockaddr_in serveraddr, clientaddr;  
  bzero(&serveraddr, sizeof(struct sockaddr_in));
  serveraddr.sin_family = AF_INET;
  serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
  serveraddr.sin_port = htons(6782);

  if (-1 == bind(serversock, (struct sockaddr *)&serveraddr, 
                 sizeof(struct sockaddr_in))) 
    perror("Bind");

  if (-1 == listen(serversock, SOMAXCONN))
    perror("Listen");

  FD_ZERO(&fds);
  FD_SET(serversock, &fds);

  while(1) {

    readfds = fds;
    rc = select(FD_SETSIZE, &readfds, NULL, NULL, NULL);

    if (rc == -1) {
      perror("Select");
      break;
    }

    for (i = 0; i < FD_SETSIZE; i++) {
      if (FD_ISSET(i, &readfds)) {
        if (i == serversock) {
          if (numsocks < maxsocks) {
            clientsock[numsocks] = accept(serversock,
                                      (struct sockaddr *) &clientaddr,
                                      (socklen_t *)&clientaddrlen);
            if (clientsock[numsocks] == -1) perror("Accept");
            FD_SET(clientsock[numsocks], &fds);
            numsocks++;
          } else {
            printf("Ran out of socket space.
");

          }
        } else {
          int messageLength = 5;
          char message[messageLength+1];
          int in, index = 0, limit = messageLength+1;

          while ((in = recv(clientsock[i], &message[index], limit, 0)) > 0) {
            index += in;
            limit -= in;
          }

          printf("%d
", index);
          printf("%s
", message);

        }
      }
    }
  }

  close(serversock);
  return 0;
}

一旦客户端连接并发送了它的第一条消息，服务器就会在无限循环中运行，并从消息数组中吐出垃圾.recv 似乎没有收到任何东西.谁能看到我哪里出错了?

As soon as a client connects and sends its first message, the server just runs in an infinite loop, and spits out garbage from the message array. recv doesn't seem to receive anything. Can anyone see where i go wrong?

推荐答案

你的代码中有两个问题:

Two issues in your code:

• 你应该使用 recv(i, ...) 而不是 recv(clientsock[i], ...)

之后您不检查 recv() 是否失败，因此 printf() 打印出未初始化的缓冲区 message，因此输出中的垃圾

After that you do not check if recv() failed, and therefore printf() prints out the uninitialised buffer message, hence the garbage in the output

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