trusty (3) gethostbyaddr.3posix.gz

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 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
       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 Technology -- 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 .