gethostbyaddr man page on NeXTSTEP

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GETHOSTBYNAME(3N)					     GETHOSTBYNAME(3N)

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 NetInfo  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
		    compatibility.

       When using the name server, 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
       ``HOSTALAIASES''	 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.

       Gethostbyaddr  expects addr to be a sequence of len bytes, which should
       be set according to type.  For example, an AF_INET address should be  a
       struct  in_addr	defining  an  internet	address.   You	could get this
       information from a string in ``.'' notation by calling inet_addr (3N):

	      struct in_addr hostaddr;
	      struct hostent *host;

	      hostaddr.s_addr = inet_addr("127.23.4.34");
	      host = gethostbyaddr((char *)&myaddr, sizeof(myaddr), AF_INET);

       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 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 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 - if NetInfo is not running

SEE ALSO
       resolver(3), hosts(5), netinfo(5), hostname(7), named(8)

CAVEAT
       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	 April 5, 1988		     GETHOSTBYNAME(3N)
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