44e
/* Gets the host name for a given address */

#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>

main(int argc, char **argv)
{
	struct hostent h_ent, *hp;
	extern int h_errno;
	char addrs[50], *p;
	char addr[4];

	if (argc < 2) {
		printf("usage: gethostname <ip_addr>\n");
		exit(1);
	}

	strcpy(addrs, argv[1]);

	if ((p = strtok(addrs, ".")) == NULL) 
		goto err_exit;	
	addr[0] = (char)atoi(p);
	if ((p = strtok(NULL, ".")) == NULL) 
		goto err_exit;	
	addr[1] = (char)atoi(p);
	if ((p = strtok(NULL, ".")) == NULL) 
		goto err_exit;	
	addr[2] = (char)atoi(p);
	if ((p = strtok(NULL, "\n")) == NULL) 
		goto err_exit;	
	addr[3] = (char)atoi(p);

	if ((hp = gethostbyaddr(addr, 4, AF_INET)) == NULL) {
		printf("gethostbyaddr error, h_errno %d\n", h_errno);
		exit(1);
	}

	h_ent = *hp;
	if  (strchr(h_ent.h_name, '.')) 
		h_ent.h_name[(int)strchr(h_ent.h_name, '.') - 
			(int)h_ent.h_name] = 0;
	printf("%s", h_ent.h_name);
	exit(0);

err_exit:
	printf("Invalid address.\n");
	exit(1);
}
.

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