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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 dif-
       fer (consult 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 guar-
       anteed 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 argument 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  nota-
       tion 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 information 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 subsequent calls to any of these functions.

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

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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (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 Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                    GETHOSTBYADDR(3P)