gistfile1.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


struct sockaddr_in localSock;
struct ip_mreq group;
int sd;
int datalen;
char databuf[1500];


int main(int argc, char *argv[])
{
    sd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sd < 0){
        perror("Opening datagram socket error");
        exit(1);
    } else
        printf("Opening datagram socket....OK.\n");

    {
        int reuse = 1;
        if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0){
            perror("Setting SO_REUSEADDR error");
            close(sd);
            exit(1);
        } else
            printf("Setting SO_REUSEADDR...OK.\n");
    }


    memset((char *) &localSock, 0, sizeof(localSock));
    localSock.sin_family = AF_INET;
    localSock.sin_port = htons(4321);
    localSock.sin_addr.s_addr = INADDR_ANY;
    if(bind(sd, (struct sockaddr*)&localSock, sizeof(localSock))){
        perror("Binding datagram socket error");
        close(sd);
        exit(1);
    } else
        printf("Binding datagram socket...OK.\n");

    group.imr_multiaddr.s_addr = inet_addr("226.1.1.1");
    group.imr_interface.s_addr = inet_addr("192.168.176.129");
    if(setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0){
        perror("Adding multicast group error");
        close(sd);
        exit(1);
    } else
        printf("Adding multicast group...OK.\n");

    datalen = sizeof(databuf);
    if(read(sd, databuf, datalen) < 0){
        perror("Reading datagram message error");
        close(sd);
        exit(1);
    } else {
        printf("Reading datagram message...OK.\n");
        printf("The message from multicast server is: %d\n", datalen);
    }
 
    return 0;
}