# 2.11BSD#431 - /usr/man/cat3/gethostbyaddr.0

    GETHOSTBYNAME(3)    UNIX 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(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.

    Printed 11/26/99	October 30, 1996			1

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

         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 gethost-
         byname 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  tem-
         porary  failure  or an invalid or unknown host.  The routine
         herror can be used to print an error message 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  authorita-
    			  tive	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

    Printed 11/26/99	October 30, 1996			2

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

    			  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 for-
         mat is currently understood.

    Printed 11/26/99	October 30, 1996			3

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