NAME
gethostbyname, gethostbyaddr, sethostent, endhostent, herror
- get network host entry
SYNOPSIS
#include <netdb.h>
extern int h_errno;
struct hostent *gethostbyname(const char *name));
#include <sys/socket.h> /* for AF_INET
struct hostent *gethostbyaddr(const char *addr, int len, int type
void sethostent(int stayopen));
void endhostent(void);
void herror(const char *s);
DESCRIPTION
The gethostbyname() function returns a structure of type
hostent for the given host name. Here name is either a host
name, or an IPv4 address in standard dot notation, or an
IPv6 address in colon (and possibly dot) notation. (See RFC
1884 for the description of IPv6 addresses.) If name is an
IPv4 or IPv6 address, no lookup is performed and gethost-
byname() simply copies name into the h_name field and its
struct in_addr equivalent into the h_addr_list[0] field of
the returned hostent structure. If name doesn't end in a
dot and the environment variable HOSTALIASES is set, the
alias file pointed to by HOSTALIASES will first be searched
for name. (See hostname(7) for the file format.) The
current domain and its parents are searched unless name ends
in a dot.
The gethostbyaddr() function returns a structure of type
hostent for the given host address addr of length len and
address type type. The only valid address type is currently
AF_INET.
The sethostent() function specifies, if stayopen is true
(1), that a connected TCP socket should be used for the name
server queries and that the connection should remain open
during successive queries. Otherwise, name server queries
will use UDP datagrams.
The endhostent() function ends the use of a TCP connection
for name server queries.
The herror() function prints the error message associated
with the current value of h_errno on stderr.
The domain name queries carried out by gethostbyname() and
gethostbyaddr() use a combination of any or all of the name
server named(8), a broken out line from /etc/hosts, and the
Network Information Service (NIS or YP), depending upon the
contents of the order line in /etc/host.conf. (See
resolv+(8)). The default action is to query named(8), fol-
lowed by /etc/hosts.
The hostent structure is defined in <netdb.h> as follows:
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 */
}
#define h_addr h_addr_list[0] /* for backward compatibility */
The members of the hostent structure are:
h_name
The official name of the host.
h_aliases
A zero-terminated array of alternative names for the
host.
h_addrtype
The type of address; always AF_INET at present.
h_length
The length of the address in bytes.
h_addr_list
A zero-terminated array of network addresses for the
host in network byte order.
h_addr
The first address in h_addr_list for backward compati-
bility.
RETURN VALUE
The gethostbyname() and gethostbyaddr() functions return the
hostent structure or a NULL pointer if an error occurs. On
error, the h_errno variable holds an error number.
ERRORS
The variable h_errno can have the following values:
HOST_NOT_FOUND
The specified host is unknown.
NO_ADDRESS
The requested name is valid but does not have an IP
address.
NO_RECOVERY
A non-recoverable name server error occurred.
TRY_AGAIN
A temporary error occurred on an authoritative name
server. Try again later.
FILES
/etc/host.conf
resolver configuration file
/etc/hosts
host database file
CONFORMING TO
BSD 4.3
SEE ALSO
resolver(3), hosts(5), hostname(7), resolv+(8), named(8)