gethostbynameandgethostbyaddr.c

getAddrByName（）的一个应用Demo

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
int main(int argc ,char *argv[]) 
{ 
        struct sockaddr_in addr; 
        struct hostent *host; 
        char **alias; 
         
        if(argc!=2) 
        { 
         fprintf(stderr,"Usage:%s hostname|ip..\n\a",argv[0]); 
         exit(1); 
        } 
         
        /* 这里我们假设是IP，通过IP获得主机信息*/    
        if(inet_aton(argv[1],&(addr.sin_addr))!=0) 
        { 
           host=gethostbyaddr((char *)&(addr.sin_addr),4,AF_INET);  
           printf("Address information of Ip %s\n",argv[1]);  
        }  
        else  
        {
        /* 否则用户应该输入的是域名，通过域名找主机信息*/ 
           host=gethostbyname(argv[1]);
           printf("Address information of host %s\n",argv[1]);  
        } 
        if(host==NULL) 
        { 
        /* 找不到相关信息*/ 
           printf("No Information found");
           exit(1);
        }
        /*打印主机正式名称*/
        printf("Official host name:\n%s\n\n",host->h_name); 
        /*打印主机其他名称*/
        printf("Name aliases:\n"); 
        for(alias=host->h_aliases;*alias!=NULL;alias++) 
        printf("%s\n",*alias); 
        /*打印主机系列IP*/
        printf("\nIp address:\n"); 
        for(alias=host->h_addr_list;*alias!=NULL;alias++) 
        printf("%s\n",inet_ntoa(*(struct in_addr *)(*alias))); 
}