GETHOSTBYADDR(3P)                                   POSIX Programmer's Manual                                  GETHOSTBYADDR(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       gethostbyaddr, gethostbyname - network host database functions

SYNOPSIS
       #include <netdb.h>



       struct hostent *gethostbyaddr(const void *addr, socklen_t len,
              int type);
       struct hostent *gethostbyname(const char *name);


DESCRIPTION
       These  functions  shall  retrieve information about hosts. This information is considered to be stored in a database that
       can be accessed sequentially or randomly. Implementation of this database is unspecified.

       Note:  In many cases it is implemented by the Domain Name System, as documented in RFC 1034, RFC 1035, and RFC 1886.


       Entries shall be returned in hostent structures.

       The gethostbyaddr() function shall return an entry containing addresses of address family type for the host with  address
       addr.  The  len  argument contains the length of the address pointed to by addr. The gethostbyaddr() function need not be
       reentrant. A function that is not required to be reentrant is not required to be thread-safe.

       The gethostbyname() function shall return an entry containing addresses of address family AF_INET for the host with  name
       name.  The  gethostbyname()  function  need  not  be  reentrant.   A function that is not required to be reentrant is not
       required to be thread-safe.

       The addr argument of gethostbyaddr() shall be an in_addr structure when type is AF_INET.  It  contains  a  binary  format
       (that  is,  not  null-terminated) address in network byte order. The gethostbyaddr() function is not guaranteed to return
       addresses of address families other than AF_INET, even when such addresses exist in the database.

       If gethostbyaddr() returns successfully, then the h_addrtype field in the result shall be the same as the  type  argument
       that  was  passed to the function, and the h_addr_list field shall list a single address that is a copy of the addr argu-
       ment that was passed to the function.

       The name argument of gethostbyname() shall be a node name; the behavior of gethostbyname() when passed a numeric  address
       string  is  unspecified.  For  IPv4,  a  numeric  address  string  shall  be  in the dotted-decimal notation described in
       inet_addr() .

       If name is not a numeric address string and is an alias for a valid host name, then gethostbyname() shall return informa-
       tion about the host name to which the alias refers, and name shall be included in the list of aliases returned.

RETURN VALUE
       Upon  successful  completion,  these  functions  shall return a pointer to a hostent structure if the requested entry was
       found, and a null pointer if the end of the database was reached or the requested entry was not found.

       Upon unsuccessful completion, gethostbyaddr() and gethostbyname() shall set h_errno to indicate the error.

ERRORS
       These functions shall fail in the following cases. The gethostbyaddr() and gethostbyname() functions shall set h_errno to
       the value shown in the list below. Any changes to errno are unspecified.

       HOST_NOT_FOUND

              No such host is known.

       NO_DATA
              The  server  recognized the request and the name, but no address is available. Another type of request to the name
              server for the domain might return an answer.

       NO_RECOVERY

              An unexpected server failure occurred which cannot be recovered.

       TRY_AGAIN
              A temporary and possibly transient error occurred, such as a failure of a server to respond.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The gethostbyaddr() and gethostbyname() functions may return pointers to static data, which may be overwritten by  subse-
       quent calls to any of these functions.

       The getaddrinfo() and getnameinfo() functions are preferred over the gethostbyaddr() and gethostbyname() functions.

RATIONALE
       None.

FUTURE DIRECTIONS
       The gethostbyaddr() and gethostbyname() functions may be withdrawn in a future version.

SEE ALSO
       endhostent(),  endservent(),  gai_strerror(),  getaddrinfo(),  h_errno(),  inet_addr(),  the  Base  Definitions volume of
       IEEE Std 1003.1-2001, <netdb.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy  between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                             GETHOSTBYADDR(3P)