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NAME
gethostbyname, gethostbyaddr, herror, hstrerror - get network host entry
SYNOPSIS
#include <network.h>
struct hostent *gethostbyname(const char *name);
struct hostent *gethostbyaddr(const char *addr, int len, int type);
void herror(const char *s);
const char * hstrerror(int err);
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
gethostbyname() 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 for
mat.) 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 cur
rently AF_INET.
The (obsolete) herror() function prints the error message
associated with the current value of h_errno on stderr.
The (obsolete) hstrerror() function takes an error number
(typically h_errno) and returns the corresponding message
string.
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), followed 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 com
patibility.
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 or NO_DATA
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.
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