getipnodebyname(SLIB)

Syntax

   cc ... -lsocket
   

   #include <netdb.h>
   

   struct hostent *
   getipnodebyname(const char *name, int af, int flags, int *error);
   

   struct hostent *
   getipnodebyaddr(const void *addr, size_t len, int af, int *error);
   

   void
   freehostent(struct hostent *he);
   

Description

   getipnodebyname(), and getipnodebyaddr() each return a pointer to a hos-
   tent 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, named(ADMN),  or bro-
   ken-out fields from a line in /etc/hosts. If the local name server is not
   running, these routines do a lookup in /etc/hosts.
   

         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.
   

   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.
   

   This structure should be freed after use by calling freehostent().
   

   When using the nameserver, getiphostbyaddr() will search for the named
   host in each parent domain given in the ``search'' directive of
   resolver(SLIB) 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 match-
   ing the input name.  See hostname(ADMN) for the domain search procedure and
   the alias file format.
   

   Getiphostbyaddr() can be told to look for IPv4 addresses, IPv6 addresses
   or both IPv4 and IPv6.  If IPv4 addresses only are to be looked up then
   af should be set to AF_INET, otherwise it should be set to AF_INET6.
   

   There are three flags that can be set
   

   AI_V4MAPPED    Return IPv4 addresses if no IPv6 addresses are found.
                  This flag is ignored unless af is AF_INET6.
   

   AI_ALL         Return IPv4 addresses as well IPv6 addresses if
                  AI_V4MAPPED is set.  This flag is ignored unless af is
                  AF_INET6.
   

   AI_ADDRCONFIG  Only return addresses of a given type if the system has an
                  active interface with that type.
   

   Also AI_DEFAULT is defined to be (AI_V4MAPPED|AI_ADDRCONFIG).
   

   Getipnodebyaddr() will lookup IPv4 mapped and compatible addresses in the
   IPv4 name space and IPv6 name space
   

   Freehostent() frees the hostent structure allocated be getipnodebyname()
   and getipnodebyaddr().  The structures returned by gethostbyname(),
   gethostbyname2(), gethostbyaddr() and gethostent() should not be passed
   to freehostent() as they are pointers to static areas.
   

Environment

   HOSTALIASES    Name of file containing (host alias, full hostname) pairs.
   

Files

   /etc/hosts     See hosts(SFF).

Diagnostics

   Error return status from getipnodebyname() and getipnodebyaddr() is indi-
   cated by return of a null pointer.  In this case error may then be
   checked to see whether this is a temporary failure or an invalid or un-
   known host.  errno can have the following values:
   

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

         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 ex-
                           pect.
   

         NO_ADDRESS        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

   hosts(SFF), hostname(ADMN), named(ADMN), resolver(SFF), resolver(SLIB),
   gethostbyname(SLIB), RFC2553.
   

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