GETHOSTBYNAME(3)        NetBSD Library Functions Manual       GETHOSTBYNAME(3)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #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);

     struct hostent *
     gethostent(void);

     void
     sethostent(int stayopen);

     void
     endhostent(void);

     void
     herror(const char *string);

     const char *
     hstrerror(int err);

DESCRIPTION
     The gethostbyname(), gethostbyname2() and gethostbyaddr() functions each
     return a pointer to an object with the following structure describing an
     internet host.

     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
                  AF_INET.

     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 com-
                  patibility.

     In the case of gethostbyname() and gethostbyname2(), the host is speci-
     fied by name, or using a string representation of a numeric address.  In
     the case of gethostbyaddr(), the host is specified using a binary repre-
     sentation of an address.

     The returned struct hostent structure may contain the result of a simple
     string to binary conversion, information obtained from the domain name
     resolver (see resolver(3)), 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).

     When using the domain name resolver, 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 function will return NULL after having set h_errno
     to NETDB_INTERNAL.

     The gethostent() function reads the next line of the /etc/hosts file,
     opening the file if necessary.

     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 consist-
     ing 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 cor-
     responding to the value of the err parameter.

FILES
     /etc/hosts

DIAGNOSTICS
     Error return status from gethostbyent(), 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 authori-
                     tative 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
     resolver(3), hosts(5), nsswitch.conf(5), hostname(7), named(8)

HISTORY
     The herror() function appeared in 4.3BSD.  The endhostent(),
     gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func-
     tions appeared in 4.2BSD.  The gethostbyname2() function first appeared
     in bind-4.9.4.  IPv6 support was implemented in WIDE Hydrangea IPv6 pro-
     tocol stack kit.

CAVEATS
     If the search routines specified in nsswitch.conf(5) decide to read the
     /etc/hosts file, gethostbyname(), gethostbyname2(), and gethostbyaddr()
     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(), gethostbyaddr(), or
     gethostent().

     The endhostent() function closes the file.

BUGS
     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.

     The gethostent() does not currently follow the search order specified in
     nsswitch.conf(5) and only reads the /etc/hosts file.

NetBSD 5.0.1                    October 7, 2006                   NetBSD 5.0.1

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