select_t.c

#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>


#include <sys/socket.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>


#define SOCKET_ERROR   ((int)-1)
#define MAXFD 10
#define BUFSIZE 10000


int new_listener(unsigned short int local_port_number){

    struct sockaddr_in Local, From;
    int socketfd,ris;
    socketfd = socket(AF_INET,SOCK_DGRAM,0);
    if (socketfd == SOCKET_ERROR) {
        printf ("socket() failed, Err: %d \"%s\"\n", errno,strerror(errno));
        exit(1);
    }

    memset(&Local, 0,sizeof(Local));
    Local.sin_family =AF_INET;
    Local.sin_addr.s_addr=inet_addr("127.0.0.1");
    Local.sin_port=htons(local_port_number);
    ris=bind(socketfd,(struct sockaddr*)&Local,sizeof(Local));
    if (ris == SOCKET_ERROR)  {
        printf ("bind() 1 failed, Err: %d \"%s\"\n",errno,strerror(errno));
        exit(1);
    }

}


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

    char buffer[BUFSIZE];
    fd_set rfds,wfds;
    struct timeval tv;
    int i,msglen,h[MAXFD],retval;

    FD_ZERO(&rfds);
    for(i=1;i<argc;i++){
        h[i-1]=new_listener(atoi(argv[i]));
        FD_SET(h[i-1], &rfds);
    }

    FD_ZERO(&wfds);
    FD_SET(1,&wfds);

    /* Wait up to five seconds. */
    tv.tv_sec = 5;
    tv.tv_usec = 0;

    retval = select(1, &rfds, &wfds, NULL, &tv);
    /* Don’t rely on the value of tv now! */

    if (retval == -1)
        perror("select()");
    else if (retval){
        printf("Data is available now.\n");
        for(i=1;i<argc;i++){
            if (FD_ISSET(h[i-1], &rfds)){
                msglen=recv(h[i-1], buffer, BUFSIZE, 0);
                if (msglen>=0) printf("%s\n",buffer);
            }
        }
    }
    else
        printf("No data within five seconds.\n");


    return 0;
}