组播（多播）

struct sockaddr_in remoteAddr;

memset(remoteAddr.sin_zero, 0, sizeof(remoteAddr.sin_zero));
remoteAddr.sin_family = AF_INET;  /* 建立新的连接 */
//remoteAddr.sin_family = AF_INET;  /* 断开旧的连接 */
inet_pton(AF_INET,player->rtpUdp.rip, &remoteAddr.sin_addr);
remoteAddr.sin_port = htons(player->rtpUdp.rport);   //port: 0
do {
    ret = connect(player->rtpUdp.fd,(struct sockaddr *)&remoteAddr,remoteAddrLen);
} while(ret == -1 && errno == EINTR);

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

#define BUFLEN 255

#if 0
#define VX_RTP_MUL_IP	"239.0.0.11"
#define VX_RTP_LOCAL_PORT 15550
#else
#define VX_RTP_MUL_IP	"225.0.0.37"
#define VX_RTP_LOCAL_PORT 12345
#endif

static int socket_set_nonblock(int s)
{
	int flags, res;

	flags = fcntl(s, F_GETFL, 0);
	if (flags < 0) {
		flags = 0;
	}

	res = fcntl(s, F_SETFL, flags | O_NONBLOCK);
	if (res < 0) {
		printf( "fcntl return err:%d!\n", res);
		return -1;
	}

	return 0;
}

int main (int argc, char **argv)
{
	int fd = -1;
	int ret = -1, n = 0, sock_len = 0;
	char recmsg[BUFLEN + 1];
	fd_set rfds;
	struct sockaddr_in addr;
	struct timeval tv;
	struct ip_mreq mreq;
	int yes=1;
	int loop = 0;

	/*UDP*/
	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if(fd == -1) {
		printf("create udp socket error %d", -errno);
		return -1;
	}

	socket_set_nonblock(fd);

	/* 允许多个应用绑定同一个本地端口接收数据包 */
	ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes,sizeof(yes));
	if (ret < 0) {
		printf("setsockopt: SO_REUSEADDR error, ret=%d\n", ret);
		goto failed;
	}

	/* 禁止组播数据回环 */
	if( setsockopt(fd, IPPROTO_IP, IP_MULTICAST_LOOP, (char *)&loop, sizeof(loop)) < 0 ){
		printf("setsockopt: IP_MULTICAST_LOOP error, ret=%d\n", ret);
		goto failed;
	}

	/* 加入组播 */
	mreq.imr_multiaddr.s_addr=inet_addr(VX_RTP_MUL_IP);
	mreq.imr_interface.s_addr=htonl(INADDR_ANY);
	ret = setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq));
	if (ret < 0) {
		printf("setsockopt: IP_ADD_MEMBERSHIP error, ret=%d\n", ret);
		goto failed;
	}

	memset(addr.sin_zero, 0, sizeof(addr.sin_zero));
	addr.sin_family = AF_INET;
	addr.sin_addr.s_addr = htonl(INADDR_ANY);
	addr.sin_port = htons(VX_RTP_LOCAL_PORT);

	/* 设置网卡的组播IP !!! */
	ret = inet_pton(AF_INET, VX_RTP_MUL_IP, &addr.sin_addr);
	if (ret <= 0) {
		printf("Set network card multicast ip error, ret=%d\n", ret);
		goto failed;
	}

	/* 绑定网卡 */
	ret = bind(fd, (const struct sockaddr *)&addr, sizeof(addr));
	if (ret < 0) {
		printf("Bind socket error, ret=%d\n", ret);
		goto failed;
	}

	printf("create rtp udp socket %d ok\n",fd);

	sock_len = sizeof(addr);
	/* 循环接收网络上来的组播消息 */
	for (;;)
	{
		tv.tv_sec = 1;
		tv.tv_usec = 0;

		FD_ZERO(&rfds);
		FD_SET(fd, &rfds);

		ret = select(fd + 1, &rfds, NULL, NULL, &tv);
		if (-1 == ret) {
			printf("===> func: %s, line: %d, Socket select error\n", __func__, __LINE__);
			return -1;
		} else if (0 == ret) {
			printf("===> func: %s, line: %d, select timeout\n", __func__, __LINE__);
			continue;
		}
		//struct sockaddr_in tmp_addr;
		//socklen_t addr_len = sizeof(tmp_addr);
		//bzero (recmsg, BUFLEN + 1);

eagain:
		//n = recvfrom(fd, recmsg, BUFLEN, 0, (struct sockaddr*) &addr, (socklen_t*)&sock_len);
		//n = recvfrom(fd, recmsg, BUFLEN, 0, (struct sockaddr*) &tmp_addr, &addr_len);
		n = recv(fd, recmsg, BUFLEN, 0);
		if (n < 0) {
			printf("recvfrom err in udptalk!, n: %d, errno: %d\n", n, -errno);
			if (EAGAIN == errno)
				goto eagain;
			else
				return -1;
		} else if (n == 0) {
			printf("recv data siez: %d\n", n);
		} else {
			/* 成功接收到数据报 */
			unsigned int * tmp = (unsigned int*)recmsg;

			printf ("s: %d, peer: 0x%08x\n", n, tmp[0]);
		}

	}

	return 0;

failed:
	if(fd > 0)
		close(fd);
	return -1;
}

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

#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"

int main(int argc, char *argv[])
{
	struct sockaddr_in addr;
	int fd;
	char *message="Hello, World!";

	/* create what looks like an ordinary UDP socket */
	if ((fd=socket(AF_INET,SOCK_DGRAM,0)) < 0)
	{
		perror("socket");
		exit(1);
	}

	/* set up destination address */
	memset(&addr,0,sizeof(addr));
	addr.sin_family=AF_INET;
	addr.sin_addr.s_addr=inet_addr(HELLO_GROUP);
	addr.sin_port=htons(HELLO_PORT);

	printf("message: %s, (HEX: 0x%08x)\n", message, *(unsigned int*)message);
	/* now just sendto() our destination! */
	while (1)
	{
		if (sendto(fd,message, strlen(message), 0, (struct sockaddr *) &addr, sizeof(addr)) < 0)
		{
			perror("sendto");
			exit(1);
		}
		sleep(1); //会影响接受端select的超时时间，延时越大，select的超时越大
	}
}