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gethostbyaddr(3)					      gethostbyaddr(3)

       gethostbyaddr, gethostbyaddr_r - Get a network host entry by address

       #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	 back‐
       ward compatibility (see standards(5)): struct hostent *gethostbyaddr(
	       const char *addr,
	       int len,
	       int type );

       Standard C Library (libc)

       Interfaces  documented on this reference page conform to industry stan‐
       dards as follows:

       gethostbyaddr():	 XNS4.0, XNS5.0

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

       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.

       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 sequen‐
       tially 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 spec‐
       ified in the /etc/resolv.conf file.  When the name server is  not  run‐
       ning, the gethostbyaddr() routine searches the local hosts name file.

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

       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 gethost‐
       byaddr_r() routine.

       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.

       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  gethost‐
       byaddr_r()  routine  sets  errno	 to the corresponding value: The name,
       hptr, or hdptr is invalid, or type is not AF_INET.

       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.

       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


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