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gethostbyaddr(3)
NAME
  gethostbyaddr, gethostbyaddr_r - Gets a network host entry by address

LIBRARY
  Standard C Library (libc.so, libc.a)

SYNOPSIS
  #include <netdb.h>

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

  [Digital]  The following obsolete function 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);

  [Digital]  The following definition of the gethostbyaddr() function  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) ;

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

  gethostbyaddr():  XPG4-UNIX

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

PARAMETERS
  addr	    Specifies an Internet address in network order.

  len	    Specifies the number of bytes in an Internet address.

  type	    Specifies the Internet domain address format. The value AF_INET
	    must be used.

  hdptr	    [Digital]  Is data for the host database.  The netdb.h header
	    file defines the hostent_data structure.

  hptr	    [Digital]  Points to the hostent structure.	 The netdb.h header
	    file defines the hostent structure.

DESCRIPTION
  The gethostbyname() function 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 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() function 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
  address parameter must specify the address in network order. The type
  parameter must be the constant AF_INET, which specifies the Internet
  address format. When EOF (End-of-File) is reached without a match, an error
  value is returned.

  If using 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() function searches the local hosts name file.

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

NOTES
  The gethostbyaddr() function returns a pointer to thread-specific data.
  Subsequent calls to this or a related function from the same thread
  overwrite this data.

  [Digital]  The gethostbyaddr_r() function is an obsolete reentrant version
  of the gethostbyaddr() function.  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() function.

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

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

ERRORS
  If the gethostbyaddr() or gethostbyaddr_r() function call fails, h_errno is
  set to one of the following values:

  [HOST_NOT_FOUND]
	    Host is unknown.

  [NO_DATA] No address is available for the name specified in the server
	    request.  This is not a soft error.	 Another type of name server
	    request may be successful.

  [NO_RECOVERY]
	    An unexpected server failure occurred.  This is a nonrecoverable
	    error.

  [TRY_AGAIN]
	    This is a soft error that indicates that the local server did not
	    receive a response from an authoritative server. A retry at some
	    later time may be successful.

  [Digital]  If any of the following conditions occurs, the gethostbyaddr_r()
  function sets errno to the corresponding value:

  [EINVAL]  The name, hptr, or hdptr is invalid, or type is not AF_INET.

FILES
  /etc/hosts
	    This file is the DARPA 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.

  /etc/resolv.conf
	    The resolver configuration file.

  /etc/svc.conf
	    The database service selection configuration file.

RELATED INFORMATION
  Functions: 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)