通过域名获取ip的代码inet_ntop

通过如“www.163.com”获取ip地址。

#include "global.h"

/*
 * @brief 通过主机名host如"www.163.com"获得ip地址
 * @param[in]  host  主机名
 * @param[out] ip    缓冲区，兼容ipv4和v6
 * @return 成功返回0，失败返回负值。
 */
int getipbyhost(char *host, unsigned char ip[INET6_ADDRSTRLEN])
{
	struct hostent *h;
	char *ptr, **pptr;
	int i;
	if (host == NULL || ip == NULL)
		return -1;
	h = gethostbyname(host);
	if (h == NULL)
		return -2;
	
	switch(h->h_addrtype)
	{
	case AF_INET:
	case AF_INET6:
		//#define h_addr h_addr_list[0] 在netdb.h中
		ptr = inet_ntop(h->h_addrtype, h->h_addr, ip, INET6_ADDRSTRLEN);
		printf("ip = %s \n", ip);	
	}

	printf("Official Hostname: %s \n", h->h_name);   //官方名字
	for (pptr = h->h_aliases; *pptr != NULL; pptr++) //别名
		printf("Alias: %s\n", *pptr);

	printf("INET6_ADDRSTRLEN: %d,  INET_ADDRSTRLEN: %d \n", 
			INET6_ADDRSTRLEN,    INET_ADDRSTRLEN);

	if (i == 32)
		printf("Warnning:Too Much ip for the host."
				" Only fetch 32 ahead this time!\n");

	return 0;
}

int main(int argc, char **argv)
{
	int ret;
	unsigned char ip[INET6_ADDRSTRLEN];
	
	if (argc != 2)
		printf("Usage: command <arg1>\n");

	getipbyhost(argv[1], ip);
	return 0;
}