GETIPNODEBYNAME(3) BSD Programmer's Manual GETIPNODEBYNAME(3)NAME
getipnodebyname, getipnodebyaddr - get network host entry
freehostent - free network host entry
SYNOPSIS
#include <netdb.h>
struct hostent *
getipnodebyname(const char *name, int af, int flags, int *error);
struct hostent *
getipnodebyaddr(const void *addr, size_t len, int af, int *error);
void
freehostent(struct hostent *he);
DESCRIPTIONGetipnodebyname(), and getipnodebyaddr() each return a pointer to a hos-
tent structure (see below) describing an internet host referenced by name
or by address, as the function names indicate. This structure contains
either the information obtained from the name server, named(8), or bro-
ken-out fields from a line in /etc/hosts. If the local name server is not
running, these routines do a lookup in /etc/hosts.
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.
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 com-
patibility.
This structure should be freed after use by calling freehostent().
When using the nameserver, getiphostbyaddr() will search for the named
host in each parent domain given in the ``search'' directive of re-
solv.conf(5) unless the name contains 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 match-
ing the input name. See hostname(7) for the domain search procedure and
the alias file format.
Getiphostbyaddr() can be told to look for IPv4 addresses, IPv6 addresses
or both IPv4 and IPv6. If IPv4 addresses only are to be looked up then
af should be set to AF_INET, otherwise it should be set to AF_INET6.
There are three flags that can be set
AI_V4MAPPED Return IPv4 addresses if no IPv6 addresses are found.
This flag is ignored unless af is AF_INET6.
AI_ALL Return IPv4 addresses as well IPv6 addresses if
AI_V4MAPPED is set. This flag is ignored unless af is
AF_INET6.
AI_ADDRCONFIG Only return addresses of a given type if the system has an
active interface with that type.
Also AI_DEFAULT is defined to be (AI_V4MAPPED|AI_ADDRCONFIG).
Getipnodebyaddr() will lookup IPv4 mapped and compatible addresses in the
IPv4 name space and IPv6 name space
Freehostent() frees the hostent structure allocated be getipnodebyname()
and getipnodebyaddr(). The structures returned by gethostbyname(),
gethostbyname2(), gethostbyaddr() and gethostent() should not be passed
to freehostent() as they are pointers to static areas.
ENVIRONMENT
HOSTALIASES Name of file containing (host alias, full hostname) pairs.
FILES
/etc/hosts See hosts(5).
HOSTALIASES Name of file containing (host alias, full hostname) pairs.
DIAGNOSTICS
Error return status from getipnodebyname() and getipnodebyaddr() is indi-
cated by return of a null pointer. In this case error may then be
checked to see whether this is a temporary failure or an invalid or un-
known host. errno can have the following values:
NETDB_INTERNAL This indicates an internal error in the library,
unrelated to the network or name service. errno
will be valid in this case; see perror(2).
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 authoritative server. A retry at some later
time may succeed.
NO_RECOVERY Some unexpected server failure was encountered.
This is a non-recoverable error, as one might ex-
pect.
NO_ADDRESS 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 ALSOhosts(5), hostname(7), named(8), resolver(3), resolver(5),
gethostbyname(3), RFC2553.
4th Berkeley Distribution September 17, 1999 2
