NAME
g_h_b_n, gethostbyname, gethostbyaddr, gethostent, sethos-
tent, endhostent, herror - get network host entry
SYNOPSIS
#include <net/gen/netdb.h>
extern int h_errno;
struct hostent *gethostbyname(name)
char *name;
struct hostent *gethostbyaddr(addr, len, type)
char *addr; int len, type;
struct hostent *gethostent()
sethostent(stayopen)
int stayopen;
endhostent()
herror(string)
char *string;
DESCRIPTION
Gethostbyname and gethostbyaddr each return a pointer to an
object with the following structure describing an internet
host referenced by name or by address, respectively. This
structure contains the information obtained from the name
server.
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses from name server */
};
#define h_addr h_addr_list[0] /* address, for backward compatibility */
The members of this structure are:
h_name Official name of the host.
h_aliases A zero terminated array of alternate names for
the host.
h_addrtype The type of address being returned; currently
always AF_INET.
h_length The length, in bytes, of the address.
h_addr_list A zero terminated array of network addresses
for the host. Host addresses are returned in
network byte order.
h_addr The first address in h_addr_list; this is for
backward compatiblity.
When using the nameserver, gethostbyname will search for the
named host in the current domain and its parents unless the
name ends in a dot. If the name contains no dot, and if the
environment variable ``HOSTALAIASES'' contains the name of
an alias file, the alias file will first be searched for an
alias matching the input name. See hostname(7) for the
domain search procedure and the alias file format.
Sethostent may be used to request the use of a connected TCP
socket for queries. If the stayopen flag is non-zero, this
sets the option to send all queries to the name server using
TCP and to retain the connection after each call to gethost-
byname or gethostbyaddr. Otherwise, queries are performed
using UDP datagrams.
Endhostent closes the TCP connection.
DIAGNOSTICS
Error return status from gethostbyname and gethostbyaddr is
indicated by return of a null pointer. The external integer
h_errno may then be checked to see whether this is a tem-
porary failure or an invalid or unknown host. The routine
herror can be used to print an error message describing the
failure. If its argument string is non-NULL, it is printed,
followed by a colon and a space. The error message is
printed with a trailing newline.
h_errno can have the following values:
HOST_NOT_FOUND No such host is known.
TRY_AGAIN This is usually a temporary error and
means that the local server did not
receive a response from an authorita-
tive server. A retry at some later
time may succeed.
NO_RECOVERY Some unexpected server failure was
encountered. This is a non-recoverable
error.
NO_DATA The requested name is valid but does
not have an IP address; this is not a
temporary error. This means that the
name is known to the name server but
there is no address associated with
this name. Another type of request to
the name server using this domain name
will result in an answer; for example,
a mail-forwarder may be registered for
this domain.
SEE ALSO
resolver(3), hostname(7), nonamed(8), named(8)
BUGS
All information is contained in a static area so it must be
copied if it is to be saved. Only the Internet address for-
mat is currently understood.