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The and functions 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, broken-out fields from a line in or database
entries supplied by the system . If the local name server is not running
these routines do a lookup in 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: Official name of the host. A
zero terminated array of alternate names for the host. The type of address
being returned; currently always The length, in bytes, of the address.
A zero terminated array of network addresses for the host. Host addresses
are returned in network byte order. The first address in this is for backward
compatibility. When using the nameserver, 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 contains the
name of an alias file, the alias file will first be searched for an alias
matching the input name. See for the domain search procedure and the alias
file format. The function may be used to request the use of a connected
socket for queries. If the flag is non-zero, this sets the option to send
all queries to the name server using and to retain the connection after
each call to or Otherwise, queries are performed using datagrams. The
function closes the connection.
Error return status
from and is indicated by return of a null pointer. The external integer
may then be checked to see whether this is a temporary failure or an invalid
or unknown host. The routine can be used to print an error message describing
the failure. If its argument is it is printed, followed by a colon and
a space. The error message is printed with a trailing newline. The routine
returns a pointer to the message string affiliated with an error number.
The array pointed to is not to be modified by the program. The variable
can have the following values: No such host is known. 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. Some
unexpected server failure was encountered. This is a non-recoverable error.
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.
The function is defined, and and are redefined, when is built
to use only the routines to lookup in and not the name server. The function
reads the next line of opening the file if necessary. The function opens
and/or rewinds the file If the argument is non-zero, the file will not
be closed after each call to or The function closes the file.
The
function appeared in The and functions appeared in
These functions
use static data storage; if the data is needed for future use, it should
be copied before any subsequent calls overwrite it. Only the Internet address
format is currently understood.
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