Chapter 8 (gethostbyname, gethostbyaddr)

<gethostbyname.c>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netdb.h>
void error_handling(char *message);

int main(int argc, char *argv[])
{
	int i;
	struct hostent *host;
	if(argc!=2) {
		printf("Usage : %s <addr>\n", argv[0]);
		exit(1);
	}
	
	host=gethostbyname(argv[1]);
	if(!host)
		error_handling("gethost... error");

	printf("Official name: %s \n", host->h_name);
	
	for(i=0; host->h_aliases[i]; i++)
		printf("Aliases %d: %s \n", i+1, host->h_aliases[i]);
	
	printf("Address type: %s \n", 
		(host->h_addrtype==AF_INET)?"AF_INET":"AF_INET6");

	for(i=0; host->h_addr_list[i]; i++)
		printf("IP addr %d: %s \n", i+1,
					inet_ntoa(*(struct in_addr*)host->h_addr_list[i]));
	return 0;
}

void error_handling(char *message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

 

<compile 결과>

 

<gethostbyaddr.c>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netdb.h>
void error_handling(char *message);

int main(int argc, char *argv[])
{
	int i;
	struct hostent *host;
	struct sockaddr_in addr;
	if(argc!=2) {
		printf("Usage : %s <IP>\n", argv[0]);
		exit(1);
	}

	memset(&addr, 0, sizeof(addr));
	addr.sin_addr.s_addr=inet_addr(argv[1]);
	host=gethostbyaddr((char*)&addr.sin_addr, 4, AF_INET);
	if(!host)
		error_handling("gethost... error");

	printf("Official name: %s \n", host->h_name);

	for(i=0; host->h_aliases[i]; i++)
		printf("Aliases %d: %s \n", i+1, host->h_aliases[i]);
	
	printf("Address type: %s \n", 
		(host->h_addrtype==AF_INET)?"AF_INET":"AF_INET6");

	for(i=0; host->h_addr_list[i]; i++)
		printf("IP addr %d: %s \n", i+1,
					inet_ntoa(*(struct in_addr*)host->h_addr_list[i]));	
	return 0;
}

void error_handling(char *message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

 

<compile 결과>