使用定时器的c-socket编程

我需要帮助在C中进行套接字编程。我需要在C中编写一个服务器客户端程序，其中两个IP在创建的套接字上相互通信。我成功地做到了这一点。但现在我想将计时器添加到套接字中。我研究了一点，发现它可以通过select（）来实现，其中我们给出了超时值。我试着做了，但没有成功。在下面显示的代码中，我尝试连接到一个客户端，并读取创建的新套接字10秒。如果客户端在这10秒内发送了一些消息，服务器应该接收该消息并发回确认。如果没有，则必须发出一条错误消息，说明超时。

我的服务器代码如下：

    #include<stdio.h>
    #include<unistd.h>
    #include<sys/time.h>
    #include<sys/types.h>
    #include<sys/socket.h>
    #include<netinet/in.h>
    #include<stdlib.h>
    void error(char *msg)
    {
        perror(msg);
        exit(1);
    }
    int main(int argc, char *argv[])
    {
        int a=1;
        fd_set readfds,writefds;
        int ready_for_reading,reading;
        struct timeval time_out;
        FD_ZERO(&readfds);
  //    FD_ZERO(&writefds);
        FD_SET(a,&readfds);
        time_out.tv_sec = 10;    // 10 seconds
        time_out.tv_usec = 0;    // 0 milliseconds
  //    ready_for_reading=select(1,&readfds,NULL,NULL,&time_out);

        int sockfd, newsockfd, portno,n,clilen;;
        struct sockaddr_in serv_addr,cli_addr;
        char buffer[256];
        portno=atoi(argv[1]);
        sockfd=socket(AF_INET,SOCK_STREAM,0);
        if(sockfd==-1)
            error("nError creating socket");
        serv_addr.sin_family=AF_INET;
        serv_addr.sin_port=htons(portno);
        serv_addr.sin_addr.s_addr=INADDR_ANY;
        n=bind(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
        if(n<0)
            error("nError binding socket");
        listen(sockfd,5);
        clilen=sizeof(cli_addr);
        printf("nAccept call reached");
        newsockfd=accept(sockfd,(struct sockaddr *)&cli_addr,&clilen);
        printf("nnewSockfd=%d",newsockfd);
        printf("ntesting value:%d",sizeof(readfds));
        if(newsockfd==-1)
            error("nError on accept");
    //  FD_SET(a,&readfds);
        ready_for_reading=select(sizeof(readfds)*8,&readfds,NULL,NULL,&time_out);
        printf("nready_for_reading=%d",ready_for_reading);
        if (ready_for_reading == -1) 
        {
            /* Some error has occured in input */
             printf("Unable to read your inputn");
             return -1;
        }
         else 
        {
                  if (ready_for_reading) 
              {
                     reading = read(newsockfd, buffer, 255);
                     printf("Read, %d bytes from input : %s n", reading,buffer);
                  } 
              else 
              {
                     printf(" 10 Seconds are over - no data input n");
             return 0;
                  }
            }
    /*  n=read(newsockfd,buffer,255);
        if(n<0)
            error("nError in reading client's msg");
    */
        printf("nClient's msg is:%sn",buffer);
        n=write(newsockfd,"I got your message",25);
        if(n<0)
            error("nError on writing");
        return 0;
    }

select（）函数始终返回"0"。我需要帮助。提前感谢，理查德。

      int a=1;
      fd_set readfds,writefds;
      int ready_for_reading,reading;
      struct timeval time_out;
      FD_ZERO(&readfds);
//    FD_ZERO(&writefds);
      FD_SET(a,&readfds); // a?!

#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
ssize_t recv_with_timeout (int s, void *buf, size_t len, int flags,
                           struct timeval *timeout)
{
    if (timeout) {
        ssize_t bytes;
        int r;
        struct timeval last;
        socklen_t lastlen = sizeof(last);
        r = getsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &last, &lastlen);
        if (r < 0) return r;
        r = setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, timeout, sizeof(*timeout));
        if (r < 0) return r;
        bytes = recv(s, buf, len, flags);
        r = setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &last, lastlen);
        assert(r == 0);
        return bytes;
    }
    return recv(s, buf, len, flags);
}