NAME    [Toc]    [Back]

       gethostbyaddr,  gethostbyaddr_r - Get a network host entry
       by address

SYNOPSIS    [Toc]    [Back]

       #include <netdb.h>

       struct hostent *gethostbyaddr(
               const void *addr,
               size_t len,
               int type );

       [Tru64 UNIX]  The following obsolete routine is  supported
       in  order to maintain backward compatibility with previous
       versions of the operating system.  You should not  use  it
       in new designs.  int *gethostbyaddr_r(
               const char *addr,
               int len,
               int type,
               struct hostent *hptr,
               struct hostent_data *hdptr );

       [Tru64  UNIX]  The  following  definition  of the gethostbyaddr()
 routine  does not conform  to  current  standards
       and  is  supported  only  for  backward compatibility (see
       standards(5)): struct hostent *gethostbyaddr(
               const char *addr,
               int len,
               int type );

LIBRARY    [Toc]    [Back]

       Standard C Library (libc)

STANDARDS    [Toc]    [Back]

       Interfaces documented on this reference  page  conform  to
       industry standards as follows:

       gethostbyaddr():  XNS4.0, XNS5.0

       Refer to the standards(5) reference page for more information
 about industry standards and associated tags.

PARAMETERS    [Toc]    [Back]

       Specifies an Internet address in network order.  Specifies
       the number of bytes in an Internet address.  Specifies the
       Internet  domain   address   format   (AF_INET).    [Tru64
       UNIX]  Is  data for the host database.  The netdb.h header
       file   defines   the   hostent_data   structure.    [Tru64
       UNIX]  Points  to  the  hostent  structure.   The  netdb.h
       header file defines the hostent structure.

DESCRIPTION    [Toc]    [Back]

       The gethostbyaddr() routine returns a pointer to a  structure
  of  type hostent.  Its members specify data obtained
       from either the local /etc/hosts file or one of the  files
       distributed by DNS/BIND or NIS. To determine which file or
       files to search, and in which order, the system  uses  the
       switches  in  the  /etc/svc.conf file.  The netdb.h header
       file defines the hostent structure.

       The gethostbyaddr()  routine  searches  the  network  host
       database sequentially until a match with the addr and type
       parameters occurs.  The len  parameter  must  specify  the
       number  of bytes in an Internet address.  The addr parameter
 must specify the address in network order.   The  type
       parameter  must  be  the constant AF_INET, which specifies
       the Internet Protocol Version  4  (IPv4)  address  format.
       When  EOF  (End-of-File)  is  reached  without a match, an
       error value is returned.

       If using DNS/BIND, the information is obtained from a name
       server  specified  in the /etc/resolv.conf file.  When the
       name server is not running,  the  gethostbyaddr()  routine
       searches the local hosts name file.

       Use the endhostent() routine to close the /etc/hosts file.

NOTES    [Toc]    [Back]

       The gethostbyaddr() routine returns a pointer  to  threadspecific
  data. Subsequent calls to this or a related routine
 from the same thread overwrite this data.

       [Tru64 UNIX]  The gethostbyaddr_r() routine is an obsolete
       reentrant  version  of the gethostbyaddr() routine.  It is
       supported in order to maintain backward compatibility with
       previous  versions  of the operating system and should not
       be used in new designs.  Note that you must zero-fill  the
       hdptr  structure  before  its first access by the gethostbyaddr_r()
 routine.

RETURN VALUES    [Toc]    [Back]

       Upon successful completion,  the  gethostbyaddr()  routine
       returns  a  pointer to a hostent structure.  If it reaches
       the end of the network hostname  database,  it  returns  a
       null pointer.

       [Tru64  UNIX]  Upon  successful  completion,  the gethostbyaddr_r()
 routine stores the hostent structure  in  hptr,
       and returns a value of 0 (zero).  Upon failure, it returns
       a value of -1.

ERRORS    [Toc]    [Back]

       If the gethostbyaddr() or gethostbyaddr_r()  routine  call
       fails, h_errno is set to one of the following values: Host
       is unknown.  The server recognized  the  request  and  the
       name,  but  no address is available for the name.  Another
       type of name server request may be successful.   An  unexpected
  server failure occurred.  This is a nonrecoverable
       error.  A  transient  error  occurred,  for  example,  the
       server did not respond.  A retry at some later time may be
       successful.

       [Tru64 UNIX]  If any of the following  conditions  occurs,
       the  gethostbyaddr_r()  routine  sets  errno to the corresponding
 value: The name, hptr, or hdptr  is  invalid,  or
       type is not AF_INET.

FILES    [Toc]    [Back]

       This  file is the Internet network hostname database. Each
       record in the file occupies a single line  and  has  three
       fields  consisting of the host address, official hostname,
       and  aliases.   The  resolver  configuration  file.    The
       database service selection configuration file.

SEE ALSO    [Toc]    [Back]

       routines:  endhostent(3), gethostbyname(3), sethostent(3).

       Files: hosts(4), resolv.conf(4), svc.conf(4).

       Networks: bind_intro(7), nis_intro(7).

       Standards: standards(5)

       Network Programmer's Guide



                                                 gethostbyaddr(3)