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  man pages->NetBSD man pages -> gethostbyname2 (3)              



NAME    [Toc]    [Back]

     gethostbyname, gethostbyname2, gethostbyaddr, sethostent, endhostent,
     herror, hstrerror - get network host entry

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <netdb.h>
     extern int h_errno;

     struct hostent *
     gethostbyname(const char *name);

     struct hostent *
     gethostbyname2(const char *name, int af);

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

     sethostent(int stayopen);


     herror(const char *string);

     const char *
     hstrerror(int err);

DESCRIPTION    [Toc]    [Back]

     The gethostbyname(), gethostbyname2() and gethostbyaddr() functions each
     return a pointer to an object with the following structure describing an
     internet host referenced by name or by address, respectively.  This
     structure contains either the information obtained from the name server,
     named(8), broken-out fields from a line in /etc/hosts, or database
     entries supplied by the yp(8) system.  The order of the lookups is controlled
 by the `hosts' entry in nsswitch.conf(5).

     struct  hostent {
             char    *h_name;        /* official name of host */
             char    **h_aliases;    /* alias list */
             int     h_addrtype;     /* host address type */
             int     h_length;       /* length of address */
             char    **h_addr_list;  /* list of addresses from name server */
     #define h_addr  h_addr_list[0]  /* address, for backward compatibility */

     The members of this structure are:

     h_name       Official name of the host.

     h_aliases    A NULL-terminated array of alternative names for the host.

     h_addrtype   The type of address being returned; currently always

     h_length     The length, in bytes, of the address.

     h_addr_list  A NULL-terminated array of network addresses for the host.
                  Host addresses are returned in network byte order.

     h_addr       The first address in h_addr_list; this is for backward compatibility.

     When using the nameserver, gethostbyname() and gethostbyname2() will
     search for the named host in the current domain and its parents unless
     the name ends in a dot.  If the name contains no dot, and if the environment
 variable ``HOSTALIASES'' contains the name of an alias file, the
     alias file will first be searched for an alias matching the input name.
     See hostname(7) for the domain search procedure and the alias file format.

     The gethostbyname2() function is an evolution of gethostbyname() which is
     intended to allow lookups in address families other than AF_INET, for
     example AF_INET6.  Currently the af argument must be specified as AF_INET
     or AF_INET6, else the fuction will return NULL after having set h_errno

     The sethostent() function may be used to request the use of a connected
     TCP socket for queries.  If the stayopen flag is non-zero, this sets the
     option to send all queries to the name server using TCP and to retain the
     connection after each call to gethostbyname(), gethostbyname2() or
     gethostbyaddr().  Otherwise, queries are performed using UDP datagrams.

     The endhostent() function closes the TCP connection.

     The herror() function writes a message to the diagnostic output consisting
 of the string parameter s, the constant string ": ", and a message
     corresponding to the value of h_errno.

     The hstrerror() function returns a string which is the message text corresponding
 to the value of the err parameter.

FILES    [Toc]    [Back]


DIAGNOSTICS    [Toc]    [Back]

     Error return status from gethostbyname(), gethostbyname2() and
     gethostbyaddr() is indicated by return of a null pointer.  The external
     integer h_errno may then be checked to see whether this is a temporary
     failure or an invalid or unknown host.  The routine herror() can be used
     to print an error message describing the failure.  If its argument string
     is non-NULL, it is printed, followed by a colon and a space.  The error
     message is printed with a trailing newline.

     The variable h_errno can have the following values:

     HOST_NOT_FOUND  No such host is known.

     TRY_AGAIN       This is usually a temporary error and means that the
                     local server did not receive a response from an authoritative
 server.  A retry at some later time may succeed.

     NO_RECOVERY     Some unexpected server failure was encountered.  This is
                     a non-recoverable error.

     NO_DATA         The requested name is valid but does not have an IP
                     address; this is not a temporary error.  This means that
                     the name is known to the name server but there is no
                     address associated with this name.  Another type of
                     request to the name server using this domain name will
                     result in an answer; for example, a mail-forwarder may be
                     registered for this domain.

SEE ALSO    [Toc]    [Back]

     resolver(3), hosts(5), nsswitch.conf(5), hostname(7), named(8)

CAVEATS    [Toc]    [Back]

     If the search routines specified in nsswitch.conf(5) decide to read the
     /etc/hosts file, gethostbyname() and other functions will read the next
     line of the file, re-opening the file if necessary.

     The sethostent() function opens and/or rewinds the file /etc/hosts.  If
     the stayopen argument is non-zero, the file will not be closed after each
     call to gethostbyname(), gethostbyname2() or gethostbyaddr().

     The endhostent() function closes the file.

HISTORY    [Toc]    [Back]

     The herror() function appeared in 4.3BSD.  The endhostent(),
     gethostbyaddr(), gethostbyname(), and sethostent() functions appeared in
     4.2BSD.  The gethostbyname2() function first appeared in bind-4.9.4.
     IPv6 support was implemented in WIDE Hydrangea IPv6 protocol stack kit.

BUGS    [Toc]    [Back]

     These functions use static data storage; if the data is needed for future
     use, it should be copied before any subsequent calls overwrite it.  Only
     the Internet address format is currently understood.

BSD                             April 26, 2001                             BSD
[ Back ]
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