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GETHOSTBYNAME(3)	    BSD Programmer's Manual	      GETHOSTBYNAME(3)

NAME
     gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, herror
     - get network host entry

SYNOPSIS
     #include <netdb.h>

     extern int h_errno;

     struct hostent *
     gethostbyname(char *name);

     struct hostent *
     gethostbyname2(char *name, int af);

     struct hostent *
     gethostbyaddr(char *addr, int len, type);

     struct hostent *
     gethostent();

     sethostent(int stayopen);

     endhostent();

     herror(char *string);

DESCRIPTION
     Gethostbyname(), gethostbyname2(), and gethostbyaddr() each return a
     pointer to a hostent 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 broken-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; usually AF_INET.

     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.

     When using the nameserver, gethostbyname() will search for the named host
     in each parent domain given in the ``search'' directive of resolv.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 matching the in-
     put name.	See hostname(7) for the domain search procedure and the alias
     file format.

     Gethostbyname2() is an evolution of gethostbyname() intended to allow
     lookups in address families other than AF_INET, for example, AF_INET6.
     Currently, the af argument must be specified as AF_INET else the function
     will return NULL after having set h_errno to NETDB_INTERNAL.

     Sethostent() may be used to request the use of a connected TCP socket for
     queries.  If the stayopen flag is non-zero, this sets the option to send
     all queries to the name server using TCP and to retain the connection af-
     ter each call to gethostbyname() or gethostbyaddr().  Otherwise, queries
     are performed using UDP datagrams.

     Endhostent() closes the TCP connection.

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 gethostbyname() and gethostbyaddr() is indicated
     by return of a null pointer.  The external integer h_errno may then be
     checked to see whether this is a temporary failure or an invalid or un-
     known host.  The routine herror() can be used to print an error message
     describing the failure.  If its argument string is non-NULL, it is print-
     ed, followed by a colon and a space.  The error message is printed with a
     trailing newline.

     h_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_DATA	     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 ALSO
     hosts(5),	hostname(7),  named(8),	 resolver(3),  resolver(5).

CAVEAT

     Gethostent() is defined, and sethostent() and endhostent() are redefined,
     when libc is built to use only the routines to lookup in /etc/hosts and
     not the name server:

	   Gethostent() reads the next line of /etc/hosts, opening the file if
	   necessary.

	   Sethostent() is redefined to open and rewind the file.  If the
	   stayopen argument is non-zero, the hosts data base will not be
	   closed after each call to gethostbyname() or gethostbyaddr().

	   Endhostent() 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 format is currently under-
     stood.

4th Berkeley Distribution	 June 23, 1990				     3
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