Linux 网络编程之通过IP或者主机名获取信息

struct hostent
{
char *h_name; /* 主机的正式名称*/
char **h_aliases; /* 主机的别名列表*/
int h_addrtype; /* 主机的地址类型AF_INET */
int h_length; /* 主机的地址长度*/
char **h_addr_list; /* 主机的IP地址列表*/
}
#define h_addr h_addr_list[0] /* 主机的第一个IP地址*/

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

int main(int argc, char *argv[])
{
if(argc != 2)
{
printf("Usage: %s domain_name \n",argv[0]);
exit(EXIT_FAILURE);
}

struct hostent *ht = gethostbyname(argv[1]);
if( ht )
{
int i = 0;
printf("Source domain: %s \n", argv[1]);
printf("Formal domain: %s \n", ht->h_name);
printf("Address type: %s \n", \
ht->h_addrtype == AF_INET ? "AF_INET" : "AF_INET6" );
printf("Address length:%d \n", ht->h_length);

for( ; ; ++i)
{
if (ht->h_aliases[i])
printf("Aliases name %d : %s \n",i+1 ,ht->h_aliases[i]);
else
break;
}

for(i=0; ; ++i)
{
if (ht->h_addr_list[i])
printf("IP Address %d : %s \n",i+1, \
inet_ntoa((unsigned int *)ht->h_addr_list[i]));
else
break;
}

}

return 0;
}

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

#define ADDR_LEN 	4
#define ADDR_TYPE	AF_INET

int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("Usage: %s IP Address\n",argv[0]);
exit(EXIT_FAILURE);
}

struct in_addr *addr = (struct in_addr *)malloc(sizeof(struct in_addr));
if ( ! inet_aton(argv[1], addr))
{
printf(" %s Invalid address",argv[1]);
exit(EXIT_FAILURE);
}

struct hostent *ht = gethostbyaddr(addr, ADDR_LEN, ADDR_TYPE);

if(ht)
{
int i = 0;
printf("Source IP: %s\n",argv[1]);
printf("Formal domain: %s \n",ht->h_name);
printf("Address type: %s\n",ht->h_addrtype == AF_INET ? "AF_INET" : "AF_INET6");
printf("Address length: %d \n", ht->h_length);

for( ; ; ++i)
{
if(ht->h_aliases[i])
printf("Aliases name %d : %s\n",i+1,ht->h_aliases[i]);
else
break;
}

for(i = 0; ; ++i)
{
if(ht->h_addr_list[i])
printf("IP Address %d : %s\n",i+1, \
inet_ntoa((unsigned int *)ht->h_addr_list[i]));
else
break;
}
}
else
{
switch(h_errno)
{
case HOST_NOT_FOUND :
printf("The specified host is unknown\n");
break;

case NO_ADDRESS:
printf("The requested name is valid but does not have an IP address.\n");
break;

case NO_RECOVERY:
printf(" A nonrecoverable name server error occurred.\n");
break;

case TRY_AGAIN:
printf("A temporary error occurred in the authoritative \
domain name server. Please try again later.\n");
break;
}
}

return 0;
}