Question

I am building a client that can recieve information from the server and from the user (stdin), so I am using select to monitor both. What happens is that is a keyboard input is monitored the I send a message to the client and get one back, no problem. But when the server send a message nothing happens, and I don’t know why. Is using select() the proper way to do so?

Here’s my code:

void readSocket(fd_set tempfd) {
    const char * tweet, * inMessage;
    if (FD_ISSET(srverfd,&tempfd)) {
        inMessage = getMessage();
        printSystemMessages(inMessage);
    }

    if (FD_ISSET(STDIN_FILENO,&tempfd)) {
        tweet = getUserTweet();
        sendMessage(tweet);
        inMessage = getMessage();
        if (strcmp(inMessage,OK) != 0) {
            printSystemMessages(inMessage);
        }
        if (strcmp(inMessage,EXIT) == 0) {
            return;
        }
    }
    return;
}

int main (int argc, char *argv[] ){
    int value;
    bool clientON = false;
    fd_set tempfd;

    if(establishConnection(argv[2],argv[3])){
        cerr << "usage: failed to make connection" << endl << "exiting..." << endl;
        exit(EXIT_FAILURE);
    }

    cout << "Connected successfully" << endl;
    sendMessage("CONNECT "+clientName); //Connect
    if(strcmp(getMessage(),OK) == 0){
        build_select_list();
        printSystemMessages("Welcome!");
        clientON = true;
        cout<< man <<endl;
    }
    while(clientON){
        tempfd = inputFdSet;
        printTweetFormat("TweetMy:");

        value = select(maxSock, &tempfd, NULL, NULL, NULL);
        if (value < 0) {
            perror("select");
            exit(EXIT_FAILURE);
        }
        if (value == 0) {
            continue;
        }
        else {
            readSocket(tempfd);
        }
    }
    close(srverfd);

    return 0;
}

Answer 1

This might help you – pass maxSock+1 instead of maxSock to your select() call;

From the man page on select()

     nfds  is the highest-numbered file descriptor in any of the three sets,
      plus 1.