gethostbyaddr(3) - NetBSD Manual Pages

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GETHOSTBYNAME(3)          NetBSD Programmer's Manual          GETHOSTBYNAME(3)


NAME

     gethostbyname, 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 *
     gethostbyaddr(const char *addr, int 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() 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' en-
     try 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
                  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.

     When using the nameserver, gethostbyname() 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 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() or gethostbyaddr().  Other-
     wise, queries are performed using UDP datagrams.

     The endhostent() function closes the TCP connection.


FILES

     /etc/hosts


DIAGNOSTICS

     Error return status from gethostbyname() 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 un-
     known host.  The routine herror() can be used to print an error message
     describing the failure.  If its argument string is non-NULL, it is print-
     ed, followed by a colon and a space.  The error message is printed with a
     trailing newline.  The routine hstrerror() returns a pointer to the mes-
     sage string affiliated with an error number.  The array pointed to is not
     to be modified by the program.

     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 lo-
                     cal server did not receive a response from an authorita-
                     tive 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 ad-
                     dress; this is not a temporary error.  This means that
                     the name is known to the name server but there is no ad-
                     dress 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 regis-
                     tered for this domain.


SEE ALSO

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


CAVEAT

     The gethostent() function is defined, and sethostent() and endhostent()
     are redefined, when libc.a is built to use only the routines to lookup in
     /etc/hosts and not the name server.

     The gethostent() function reads the next line of /etc/hosts, 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() or gethostbyaddr().

     The endhostent() function closes the file.


HISTORY

     The herror() function appeared in 4.3BSD.  The endhostent(),
     gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func-
     tions appeared in 4.2BSD.


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.

NetBSD 1.4                     January 16, 1999                              3