C源碼:通過IP地址查找主機名 findip.c 
責任編輯：admin 　 更新日期：2005-8-6 
 
/* 
* This program is free software; you can redistribute it and/or modify 
* it under the terms of the GNU General Public License as published by 
* the Free Software Foundation; either version 2 of the License, or 
* (at your option) any later version. 
* 
* This program is distributed in the hope that it will be useful, 
* but WITHOUT ANY WARRANTY; without even the implied warranty of 
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
* GNU General Public License for more details. 
* 
* You should have received a copy of the GNU General Public License 
* along with this program; if not, write to the Free Software 
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 
* 
* 
* Filename: findip.c 
* Created : Nov. 10th 1995 @ 4:30pm 
* Author : SrfRoG (srfrog@itek.net) 
* Descrip.: This cute little program will attempt to resolve 
* an IP address to its hostname. Then prints the results 
* to standard output. 
* --------------------------------------------------------------------- 
* To compile this program: 
* Linux: gcc -O2 -m486 -s -o findip findip.c 
* AIX, BSD: gcc -O2 -s -o findip findip.c 
* SunOS: gcc -O2 -lnsl -s -o findip findip.c 
* Other: cc -o findip findip.c 
*/ 

#include 
#include 
#include 
#include 
#include 
#include 

int main(argc, argv) 
int argc; 
char **argv; 
{ 
struct hostent *ip; 
unsigned long hostname; 

if (argc != 2) 
{ 
printf("Need to specify an IP address.\n"); 
exit(1); 
} 
if ((hostname = inet_addr(argv[1])) == -1) 
{ 
printf("Could not find %s\n", argv[1]); 
exit(1); 
} 
if ((ip = gethostbyaddr((char *)&hostname, sizeof(long), AF_INET)) != NULL) 
printf("%s is %s\n", argv[1], ip->h_name); 
else 
printf("Could not resolve %s\n", argv[1]); 
return 0; 
}