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

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

       gethostbyaddr, gethostbyname - network host database functions

       #include <netdb.h>

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

       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.

       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.

       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.


              No such host is known.

              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.


              An unexpected server failure occurred which cannot be recovered.

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

       The following sections are informative.


       The gethostbyaddr() and gethostbyname() functions may return pointers to
       static data, which may be overwritten by subsequent calls to any of these

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


       The gethostbyaddr() and gethostbyname() functions may be withdrawn in a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

       endhostent(), endservent(), gai_strerror(), getaddrinfo(), h_errno(),
       inet_addr(), the Base Definitions volume of IEEE Std 1003.1-2001,

       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 .

IEEE/The Open Group                   2003                     GETHOSTBYADDR(3P)