I'm trying to connect multiple clients with this server, but the code doesn't seem to work>

Question

//////////////////////////  Server2.c ////////////////

#include<io.h>
#include<stdio.h>
#include<winsock2.h>
#include <ctype.h>
#include<string.h>
#include <sys/time.h>
#include <errno.h>



#define MY_PORT     8989 //defining the port for the socket
#define MAXBUF      256



int main(int argc , char *argv[])
{
    int a,i ;

    char str[MAXBUF];

    WSADATA wsa;
    SOCKET sockfd , clientfd;
    struct sockaddr_in self;
    int max_clients=30, client_socket[30],maxsd, sd,activ;
    char buffer[MAXBUF];
    char message[MAXBUF];

    /*set of socket descriptors will be in this */
    fd_set readfds;

    /*Initializing all client to zero */
     for (i = 0; i < max_clients; i++)
    {
        client_socket[i] = 0;
    }


    printf("\nInitialising Winsock...");
    if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
    {
        printf("Failed. Error Code : %d",WSAGetLastError());
        return 1;
    }

    printf("Initialised.\n");

    /*---create streaming socket---*/
    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
    {
        perror("Socket");
        exit(errno);
    }

        printf("Socket created.\n");

    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    /*---initialize address/port structure---*/

    self.sin_family = AF_INET;
    self.sin_port = htons(MY_PORT);
    self.sin_addr.s_addr = INADDR_ANY;

    /*---assign a port number to the socket---*/
    if ( bind(sockfd, (struct sockaddr*)&self, sizeof(self)) != 0 )
    {
        perror("socket--bind");
        exit(errno);
    }
        puts("Bind done"); //binding completed
    /*---make it a "listening socket"---*/
    if ( listen(sockfd, 3) != 0 )
    {
        perror("socket--listen");
        exit(errno);
    }

        puts("Waiting for incoming connections...");

    /*---forever... ---*/

    while (1)
    {   struct sockaddr_in client_addr;
        int addrlen=sizeof(client_addr);

        /*Clearing the socket set we created before*/
        FD_ZERO(&readfds);

        /*adding the socket we created to set*/
        FD_SET(sockfd,&readfds);
        maxsd=sockfd;
        /*Now we add the child sockets to the set */
        for ( i = 0 ; i < max_clients ; i++)
        {
            //socket descriptor
            sd = client_socket[i];

            //if valid socket descriptor then add to read list
            if(sd > 0)
                FD_SET( sd , &readfds);

            //highest file descriptor number, need it for the select function
            if(sd > maxsd)
                maxsd = sd;
        }
        /*we wait for activity on any one of the sockets, this will wait forever as timeout is NULL*/
        activ=select(maxsd+1, &readfds,NULL,NULL,NULL);

        if ((activ < 0) && (errno!=EINTR))
        {
            printf("select error");
        }

        /* If there is any sort of activity on sockfd then it will be the socket that the server has to serve */
        if (FD_ISSET(sockfd,&readfds)){
            if (clientfd= accept(sockfd, (struct sockaddr*)&client_addr, &addrlen)<0)
                {
                perror("Accept");
                exit(EXIT_FAILURE);

                }

        /*telling the user of socket number, port and ip of client*/
        printf("Connected Client\nSocket fd is %d\nIP is :%s\nPort:%d\n",clientfd,self.sin_addr.s_addr, htons(self.sin_port));

        /*adding new socket to array of sockets */
        for (i=0; i<max_clients;i++)
        {
            if(client_socket[i]==0) //if element is empty
            {
                client_socket[i]=clientfd;
                break;
            }
        }
        }
        /*else there might be some Input?output operations on some other socket*/
        for (i = 0; i < max_clients; i++)
        {
            sd=client_socket[i];
            if (FD_ISSET( sd , &readfds))
            {
                if((read(sd,buffer,MAXBUF))==0)
                {
                    printf("DISCONNECTED");

               //Close the socket and mark as 0 in list for reuse
                    close( sd );
                    client_socket[i] = 0;
                }
                else
                {
                send(clientfd,buffer, recv(clientfd, buffer, MAXBUF, 0), 0);

                }
            }
        }
    }
        /*---close connection---*/
        //close(clientfd);


    /*---clean up (should never get here!)---*/
    //close(sockfd);
        WSACleanup();
    return 0;
}

The code is for a server that accepts multiple clients and is able to tell which client is connected at a particular time. I used select() function and didn't use multithreading to have more than one client at a time. The server is able to return the port number, the address and the socket however they're not the right ones. The address turns out as null. And btw the server is supposed to send back to the client whatever the client sends it. There is another problem that I'm sort of facing right now, for some reason when I try to compile this code, into an executable file using command prompt. The created file for some reason does not open at all. I click it and it opens for a second and that's it.

Answer 1

当您从客户端读取时，无论它是哪个客户端，您总是将回复发送回clientfd （这是最后一个连接的客户端）而不是sd （您收到消息的客户端）