2.11BSD/man/cat3/gethostbyname.0
GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3)
NAME
gethostbyname, gethostbyaddr, gethostent, sethostent,
endhostent, herror - get network host entry
SYNOPSIS
#include <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
_G_e_t_h_o_s_t_b_y_n_a_m_e and _g_e_t_h_o_s_t_b_y_a_d_d_r 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 either the information obtained from the
name server, _n_a_m_e_d(8), or broken-out fields from a line in
/_e_t_c/_h_o_s_t_s. If the local name server is not running these
routines do a lookup in /_e_t_c/_h_o_s_t_s.
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.
Printed 11/26/99 October 30, 1996 1
GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3)
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, _g_e_t_h_o_s_t_b_y_n_a_m_e 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 ``HOSTALIASES'' contains the name of an
alias file, the alias file will first be searched for an
alias matching the input name. See _h_o_s_t_n_a_m_e(7) for the
domain search procedure and the alias file format.
_S_e_t_h_o_s_t_e_n_t may be used to request the use of a connected TCP
socket for queries. If the _s_t_a_y_o_p_e_n 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 _g_e_t_h_o_s_t_-
_b_y_n_a_m_e or _g_e_t_h_o_s_t_b_y_a_d_d_r. Otherwise, queries are performed
using UDP datagrams.
_E_n_d_h_o_s_t_e_n_t closes the TCP connection.
DIAGNOSTICS
Error return status from _g_e_t_h_o_s_t_b_y_n_a_m_e and _g_e_t_h_o_s_t_b_y_a_d_d_r is
indicated by return of a null pointer. The external integer
_h__e_r_r_n_o may then be checked to see whether this is a tem-
porary failure or an invalid or unknown host. The routine
_h_e_r_r_o_r can be used to print an error message describing the
failure. If its argument _s_t_r_i_n_g is non-NULL, it is printed,
followed by a colon and a space. The error message is
printed with a trailing newline.
_h__e_r_r_n_o 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
Printed 11/26/99 October 30, 1996 2
GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3)
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.
FILES
/etc/hosts
SEE ALSO
resolver(3), hosts(5), hostname(7), named(8)
CAVEAT
_G_e_t_h_o_s_t_e_n_t is defined, and _s_e_t_h_o_s_t_e_n_t and _e_n_d_h_o_s_t_e_n_t are
redefined, when _l_i_b_c is built to use only the routines to
lookup in /_e_t_c/_h_o_s_t_s and not the name server.
_G_e_t_h_o_s_t_e_n_t reads the next line of /_e_t_c/_h_o_s_t_s, opening the
file if necessary.
_S_e_t_h_o_s_t_e_n_t is redefined to open and rewind the file. If the
_s_t_a_y_o_p_e_n argument is non-zero, the hosts data base will not
be closed after each call to _g_e_t_h_o_s_t_b_y_n_a_m_e or _g_e_t_h_o_s_t_b_y_a_d_d_r.
_E_n_d_h_o_s_t_e_n_t is redefined to close the file.
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.
Printed 11/26/99 October 30, 1996 3