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

SYNOPSIS
  #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
  Standard C Library (libc)

STANDARDS
  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
  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 (AF_INET).

  hdptr
      [Tru64 UNIX]  Is data for the host database.  The netdb.h header file
      defines the hostent_data structure.

  hptr
      [Tru64 UNIX]  Points to the hostent structure.  The netdb.h header file
      defines the hostent structure.

DESCRIPTION
  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
  The gethostbyaddr() routine returns a pointer to thread-specific 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
  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
  If the gethostbyaddr() or gethostbyaddr_r() routine call fails, h_errno is
  set to one of the following values:

  [HOST_NOT_FOUND]
      Host is unknown.

  [NO_DATA]
      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.

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

  [TRY_AGAIN]
      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:

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

FILES
  /etc/hosts
      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.

  /etc/resolv.conf
      The resolver configuration file.

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

SEE ALSO
  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

Index for Section 3

Alphabetical listing for G

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