xref: /netbsd-src/external/bsd/libbind/dist/doc/gethostbyname.cat3 (revision 5bbd2a12505d72a8177929a37b5cee489d0a1cfd)

GETHOSTBYNAME(3)       FreeBSD Library Functions Manual       GETHOSTBYNAME(3)

NNAAMMEE
     ggeetthhoossttbbyynnaammee, ggeetthhoossttbbyyaaddddrr, ggeetthhoosstteenntt, sseetthhoosstteenntt, eennddhhoosstteenntt, hheerrrroorr
     -- get network host entry

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<nneettddbb..hh>>

     _e_x_t_e_r_n _i_n_t _h___e_r_r_n_o;

     _s_t_r_u_c_t _h_o_s_t_e_n_t _*
     ggeetthhoossttbbyynnaammee(_c_h_a_r _*_n_a_m_e);

     _s_t_r_u_c_t _h_o_s_t_e_n_t _*
     ggeetthhoossttbbyynnaammee22(_c_h_a_r _*_n_a_m_e, _i_n_t _a_f);

     _s_t_r_u_c_t _h_o_s_t_e_n_t _*
     ggeetthhoossttbbyyaaddddrr(_c_h_a_r _*_a_d_d_r, _i_n_t _l_e_n_, _t_y_p_e);

     _s_t_r_u_c_t _h_o_s_t_e_n_t _*
     ggeetthhoosstteenntt();

     sseetthhoosstteenntt(_i_n_t _s_t_a_y_o_p_e_n);

     eennddhhoosstteenntt();

     hheerrrroorr(_c_h_a_r _*_s_t_r_i_n_g);

DDEESSCCRRIIPPTTIIOONN
     GGeetthhoossttbbyynnaammee(), ggeetthhoossttbbyynnaammee22(), and ggeetthhoossttbbyyaaddddrr() each return a
     pointer to a _h_o_s_t_e_n_t structure (see below) describing an internet host
     referenced by name or by address, as the function names indicate.  This
     structure contains either the information obtained from the name server,
     or broken-out fields from a line in _/_e_t_c_/_h_o_s_t_s.  If the local name server
     is not running, these routines do a lookup in _/_e_t_c_/_h_o_s_t_s.

           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 zero-terminated array of alternate names for the host.

     h_addrtype   The type of address being returned; usually AF_INET.

     h_length     The length, in bytes, of the address.

     h_addr_list  A zero-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 com-
                  patibility.

     When using the nameserver, ggeetthhoossttbbyynnaammee() will search for the named host
     in each parent domain given in the ``search'' directive of resolv.conf(5)
     unless the name contains 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.

     GGeetthhoossttbbyynnaammee22() is an evolution of ggeetthhoossttbbyynnaammee() intended to allow
     lookups in address families other than AF_INET, for example, AF_INET6.
     Currently, the _a_f argument must be specified as AF_INET else the function
     will return NULL after having set _h___e_r_r_n_o to NETDB_INTERNAL.

     SSeetthhoosstteenntt() may be used to request the use of a connected TCP socket for
     queries.  If the _s_t_a_y_o_p_e_n 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 ggeetthhoossttbbyynnaammee() or ggeetthhoossttbbyyaaddddrr().  Otherwise,
     queries are performed using UDP datagrams.

     EEnnddhhoosstteenntt() closes the TCP connection.

EENNVVIIRROONNMMEENNTT
     HOSTALIASES    Name of file containing (_h_o_s_t _a_l_i_a_s, _f_u_l_l _h_o_s_t_n_a_m_e) pairs.

FFIILLEESS
     /etc/hosts     See hosts(5).

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

     _h___e_r_r_n_o can have the following values:

           NETDB_INTERNAL    This indicates an internal error in the library,
                             unrelated to the network or name service.  _e_r_r_n_o
                             will be valid in this case; see perror.

           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, as one might
                             expect.

           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.

SSEEEE AALLSSOO
     hosts(5), hostname(7), resolver(3), resolver(5).

CCAAVVEEAATT
     GGeetthhoosstteenntt() is defined, and sseetthhoosstteenntt() and eennddhhoosstteenntt() are redefined,
     when _l_i_b_c is built to use only the routines to lookup in _/_e_t_c_/_h_o_s_t_s and
     not the name server:


           GGeetthhoosstteenntt() reads the next line of _/_e_t_c_/_h_o_s_t_s, opening the file if
           necessary.

           SSeetthhoosstteenntt() is redefined to open and rewind the file.  If the
           _s_t_a_y_o_p_e_n argument is non-zero, the hosts data base will not be
           closed after each call to ggeetthhoossttbbyynnaammee() or ggeetthhoossttbbyyaaddddrr().

           EEnnddhhoosstteenntt() is redefined to close the file.

BBUUGGSS
     All information is contained in a static area so it must be copied if it
     is to be saved.  Only the Internet address format is currently under-
     stood.

4th Berkeley Distribution        June 23, 1990       4th Berkeley Distribution