GETHOSTBYNAME(3N)               Domain/OS BSD                GETHOSTBYNAME(3N)



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

SYNOPSIS
     #include <netdb.h>

     extern int h_errno;

     struct hostent *gethostbyname(name)
     char *name;

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

     struct hostent *gethostent()

     sethostent(stayopen)
     int stayopen;

     endhostent()

     herror(string)
     char *string;

DESCRIPTION
     gethostbyname and gethostbyaddr 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), or broken-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;  currently   always
                  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
                  compatiblity.

     When using the name server, 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  "HOSTALAIASES"
     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.

     sethostent 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.  Otherwise, queries
     are performed using UDP datagrams.

     endhostent closes the TCP connection.

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
     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.

     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.

Domain/OS EXTENSION
     The Domain/OS version of gethostbyname locates the name server's resolver
     routines in their own dynamic library, /lib/libresolv, rather than in the
     /lib/clib global library.

CAVEAT
     When /etc/hosts is used for name-address resolution, gethostent reads the
     next  line  of  /etc/hosts, opening the file if necessary.  sethostent is
     redefined to open and rewind the file.  If the stayopen argument is  non-
     zero,  the  hosts  database  will  not  be  closed  after  each  call  to
     gethostbyname or gethostbyaddr.  endhostent is  redefined  to  close  the
     file.

     When the name server is used for name-address resolution, gethostent does
     nothing.  sethostent  is  only  meaningful  when the stayopen argument is
     non-zero.  In that case,  the  resolver  routines  use  virtual  circuits
     rather  than  datagrams  to query the name server.  Similarly, endhostent
     turns off virtual circuit use.

BUGS
     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
     understood.

FILES
     /etc/hosts

SEE ALSO
     resolver(3), hosts(5), hostname(7), named(8)