HP-UX Reference (11i v3 07/02) - 3 Library Functions A-M (vol 6)

g
gethostent(3N) gethostent(3N)
constant AF_INET.
RETURN VALUE
If successful, gethostbyname()
, gethostbyaddr()
, and gethostent() return a pointer to the
requested
hostent structure.
gethostbyname()
and gethostbyaddr()
return NULL if their host or addr parameters, respec-
tively, cannot be found in the database. If
/etc/hosts is being used, they also return NULL if they are
unable to open
/etc/hosts .
gethostbyaddr()
also returns NULL if either its addr or len parameter is invalid.
gethostent() always returns NULL if the name server is being used.
ERRORS
If the name server is being used and
gethostbyname() or gethostbyaddr()
returns a NULL
pointer, the external integer
h_errno contains one of the following values:
HOST_NOT_FOUND
No such host is known.
TRY_AGAIN This is usually a temporary error. The local server did not receive a response
from an authoritative server. A retry at some later time may succeed.
NO_RECOVERY This is a non-recoverable error.
NO_ADDRESS The requested name is valid but does not have an IP address; this is not a
temporary error. This means another type of request to the name server will
result in an answer.
If the name server is not being used, the value of
h_errno may not be meaningful.
EXAMPLES
The following code excerpt counts the number of host entries:
int count = 0;
(void) sethostent(0);
while (gethostent() != NULL)
count++;
(void) endhostent();
The following sample program prints the canonical name, aliases, and "." separated Internet IP addresses
for a given "." separated IP address.
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
main(int argc, const char **argv)
{
u_int addr;
struct hostent *hp;
char **p;
if (argc != 2) {
(void) printf("usage: %s IP-address\n",argv[0]);
exit (1);
}
if ((int) (addr = inet_addr (argv[1])) == -1) {
(void) printf("IP-address must be of the form a.b.c.d\n");
exit (2);
}
hp=gethostbyaddr((char *) &addr, sizeof (addr), AF_INET);
if (hp == NULL) {
(void) printf("host information for %s no found \n", argv[1]);
exit (3);
520 Hewlett-Packard Company − 3 − HP-UX 11i Version 3: February 2007