GETHOSTBYNAME(3)					     Library Functions 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(name)
       char *name;

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

       struct hostent *gethostent()

       sethostent(stayopen)
       int stayopen;

       endhostent()

       herror(string)
       char *string;

DESCRIPTION

       Gethostbyname  and  gethostbyaddr 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,  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; currently always 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 compatiblity.

       When  using  the  nameserver,  gethostbyname 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 ``HOSTALIASES'' contains the name of an alias file, the alias file  will
       first be searched for an alias matching the input name.	See hostname(7) for the domain search procedure and the alias file format.

       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 after each call to gethostbyname or  gethostbyaddr.	Otherwise,
       queries are performed using UDP datagrams.

       Endhostent closes the TCP connection.

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 unknown host.  The routine herror can be used to print an error mes-
       sage  describing  the  failure.	 If its argument string is non-NULL, it is printed, followed by a colon and a space.  The error message is
       printed with a trailing newline.

       h_errno can have the following values:

	      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.

	      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.

FILES

       /etc/hosts

SEE ALSO

       resolver(3), hosts(5), hostname(7), named(8)

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
       understood.

4.2 Berkeley Distribution					 October 30, 1996						  GETHOSTBYNAME(3)