linux程序设计——数据报（第十五章）

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15.5    数据报

/*************************************************************************
 > File Name:    getdate2.c
 > Description:  getdate2.c
 > Author:       Liubingbing
 > Created Time: 2015年07月26日 星期日 15时37分05秒
 > Other:        getdate2.c
 ************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

int main(int argc, char *argv[])
{
	char *host;
	int sockfd;
	int len, result;
	struct sockaddr_in address;
	struct hostent *hostinfo;
	struct servent *servinfo;
	char buffer[128];

	if (argc == 1)
		host = "localhost";
	else
		host = argv[1];

	/* 找到主机地址,如果没有找到则报错 */
	hostinfo = gethostbyname(host);
	if (!hostinfo) {
		fprintf(stderr, "no host: %s\n", host);
		exit(1);
	}

	/* 检查主机上是否存在daytime服务 */
	servinfo = getservbyname("daytime", "udp");
	if (!servinfo) {
		fprintf(stderr, "no daytime service\n");
		exit(1);
	}
	printf("daytime port is %d\n", ntohs(servinfo->s_port));

	/* socket创建一个UDP套接字 */
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);

	/* 创建地址 */
	address.sin_family = AF_INET;
	address.sin_port = servinfo->s_port;
	address.sin_addr = *(struct in_addr *)*hostinfo->h_addr_list;
	len = sizeof(address);

	/* sendto(int sockfd, void *buffer, size_t len, int flags, struct sockaddr *, socklen_t tolen); 
	 * sendto系统调用从buffer缓存区中给使用指定套接字地址的目标服务器发送一个数据报 */
	result = sendto(sockfd, buffer, 1, 0, (struct sockaddr *)&address, len);

	/* recvfrom(int sockfd, void *buffer, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);
	 * recvfrom系统调用在套接字上等待从特定地址到来的数据报,并将它放入buffer缓存区 */
	result = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr *)&address, &len);

	buffer[result] = '\0';
	printf("read %d bytes: %s", result, buffer);

	close(sockfd);
	exit(0);
}

int sendto(int sockfd, viod *buffer, size_t len, int flags, struct sockaddr *to, socklen_t tolen);

int recvfrom(int sockfd, void *buffer, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);

15.6    小结

linux程序设计——数据报（第十五章）

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原文地址：http://blog.csdn.net/yiranant/article/details/47074661