4.3BSD-UWisc/man/cat3/gethostbyname.3n
GETHOSTBYNAME(3N) UNIX Programmer's Manual GETHOSTBYNAME(3N)
NAME
gethostbyname, gethostbyaddr, gethostent, sethostent,
endhostent - 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()
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. This structure con-
tains 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.
h_length The length, in bytes, of the address.
h_addr_list A zero terminated array of network addresses
Printed 12/27/86 May 20, 1986 1
GETHOSTBYNAME(3N) UNIX Programmer's Manual GETHOSTBYNAME(3N)
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.
_S_e_t_h_o_s_t_e_n_t allows a request for the use of a connected
socket using TCP 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.
_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.
_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 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.
FILES
/etc/hosts
SEE ALSO
hosts(5), resolver(3), 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.
Printed 12/27/86 May 20, 1986 2
GETHOSTBYNAME(3N) UNIX Programmer's Manual GETHOSTBYNAME(3N)
_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 12/27/86 May 20, 1986 3