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

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 gethost-
       byname() 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 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 unspeci-
       fied. 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 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() 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 Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications 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 Standard, 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(P)