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<h1 class="topictitle1">Example: Receive multicast datagrams </h1>
<div><p>This example enables a socket to receive multicast datagrams.</p>
<div class="section"><div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
<pre>#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
struct sockaddr_in localSock;
struct ip_mreq group;
int sd;
int datalen;
char databuf[1024];
int main (int argc, char *argv[])
{
/* ------------------------------------------------------------*/
/* */
/* Receive Multicast Datagram code example. */
/* */
/* ------------------------------------------------------------*/
/*
* Create a datagram socket on which to receive.
*/
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd < 0) {
perror("opening datagram socket");
exit(1);
}
/*
* Enable SO_REUSEADDR to allow multiple instances of this
* application to receive copies of the multicast datagrams.
*/
{
int reuse=1;
if (setsockopt(sd, SOL_SOCKET, SO_REUSEADDR,
(char *)&reuse, sizeof(reuse)) < 0) {
perror("setting SO_REUSEADDR");
close(sd);
exit(1);
}
}
/*
* Bind to the proper port number with the IP address
* specified as INADDR_ANY.
*/
memset((char *) &localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(5555);;
localSock.sin_addr.s_addr = INADDR_ANY;
if (bind(sd, (struct sockaddr*)&localSock, sizeof(localSock))) {
perror("binding datagram socket");
close(sd);
exit(1);
}
/*
* Join the multicast group 225.1.1.1 on the local 9.5.1.1
* interface. Note that this IP_ADD_MEMBERSHIP option must be
* called for each local interface over which the multicast
* datagrams are to be received.
*/
group.imr_multiaddr.s_addr = inet_addr("225.1.1.1");
group.imr_interface.s_addr = inet_addr("9.5.1.1");
if (setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP,
(char *)&group, sizeof(group)) < 0) {
perror("adding multicast group");
close(sd);
exit(1);
}
/*
* Read from the socket.
*/
datalen = sizeof(databuf);
if (read(sd, databuf, datalen) < 0) {
perror("reading datagram message");
close(sd);
exit(1);
}
}</pre>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="xmulticast.htm" title="IP multicasting provides the capability for an application to send a single IP datagram that a group of hosts in a network can receive.">Examples: Use multicasting with AF_INET</a></div>
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