linux - gethostbyname (3)
NAME
       gethostbyname, gethostbyaddr, sethostent, endhostent, her-
       ror - get network host entry
SYNOPSIS
       #include <netdb.h>
       extern int h_errno;

       struct hostent *gethostbyname(const char *name));

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

       void sethostent(int stayopen));

       void endhostent(void);

       void herror(const char *s);
DESCRIPTION
       The gethostbyname() function returns a structure  of  type
       hostent  for  the given host name.  The current domain and
       its parents are searched unless name ends in  a  dot.   If
       name  doesn't  end  in  a dot and the environment variable
       HOSTALIASES is set, the alias file pointed to  by  HOSTAL-
       IASES will first be searched for name.

       The  gethostbyaddr()  function returns a structure of type
       hostent for the given host address addr of length len  and
       address  type  type.   The only valid address type is cur-
       rently AF_INET.

       The sethostent() function specifies, if stayopen  is  true
       (1),  that  a  connected TCP socket should be used for the
       name server queries and that the connection should  remain
       open  during  successive  queries.  Otherwise, name server
       queries will use UDP datagrams.

       The endhostent() function ends the use of a TCP connection
       for name server queries.

       The  herror() function prints the error message associated
       with the current value of h_errno on stderr.

       The domain name queries carried out by gethostbyname() and
       gethostbyaddr()  use  a  combination  of any or all of the
       name server named(8), a broken out line  from  /etc/hosts,
       and the Network Information Service (NIS or YP), depending
       upon the contents of the  order  line  in  /etc/host.conf.
       (See   resolv+(8)).    The  default  action  is  to  query
       named(8), followed by /etc/hosts.

       The hostent structure is defined in <netdb.h> as follows:
              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 */
              }
              #define h_addr  h_addr_list[0]  /* for backward compatibility */

       The members of the hostent structure are:

       h_name The official name of the host.

       h_aliases
              A zero-terminated array of  alternative  names  for
              the host.

       h_addrtype
              The type of address; always AF_INET at present.

       h_length
              The length of the address in bytes.

       h_addr_list
              A  zero-terminated  array  of network addresses for
              the host in network byte order.

       h_addr The first address in h_addr_list for backward  com-
              patibility.
RETURN VALUE
       The  gethostbyname()  and gethostbyaddr() functions return
       the hostent structure  or  a  NULL  pointer  if  an  error
       occurs.   On  error,  the  h_errno variable holds an error
       number.
ERRORS
       The variable h_errno can have the following values:

       HOST_NOT_FOUND
              The specified host is unknown.

       NO_ADDRESS
              The requested name is valid but does not have an IP
              address.

       NO_RECOVERY
              A non-recoverable name server error occurred.

       TRY_AGAIN
              A temporary error occurred on an authoritative name
              server.  Try again later.
FILES
       /etc/host.conf
              resolver configuration file

       /etc/hosts
              host database file
CONFORMING TO
       BSD 4.3
SEE ALSO
       resolver(3), hosts(5), hostname(7), resolv+ (8), named(8)