10-6multicast_s.c

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

#define N 128
#define errlog(errmsg) do{perror(errmsg);\
						  printf("%s--%s--%d\n",\ 
								  __FILE__, __func__, __LINE__);\
						  exit(1);\
					     }while(0)

int main(int argc, const char *argv[])
{
	int sockfd;
	struct sockaddr_in groupcastaddr;
	socklen_t addrlen = sizeof(groupcastaddr);
	char buf[N] = {};

	if(argc < 3)
	{
		fprintf(stderr, "Usage: %s ip port\n", argv[0]);
		exit(1);
	}

	//第一步:创建套接字
	if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
	{
		errlog("fail to socket");
	}

	//第二步:填充组播网络信息结构体
	//inet_addr:将点分十进制ip地址转化为网络字节序的整型数据
	//htons:将主机字节序转化为网络字节序
	//atoi:将数字型字符串转化为整型数据
	groupcastaddr.sin_family = AF_INET;
	//224.x.x.x - 239.x.x.x
	groupcastaddr.sin_addr.s_addr = inet_addr(argv[1]);
	groupcastaddr.sin_port = htons(atoi(argv[2]));

	while(1) 
	{
		fgets(buf, N, stdin);
		buf[strlen(buf) - 1] = '\0';

		if(sendto(sockfd, buf, N, 0,\ 
				(struct sockaddr *)&groupcastaddr, addrlen) < 0)
		{
			errlog("fail to sendto");
		}

	}

	close(sockfd);

	return 0;
}