| GETHOSTBYNAME(3) | Library Functions Manual | GETHOSTBYNAME(3) | 
gethostbyname, gethostbyname2,
  gethostbyaddr, gethostent,
  sethostent, endhostent,
  herror, hstrerror —
#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
    void *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);
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:
AF_INET.In the case of gethostbyname() and
    gethostbyname2(), the host is specified by name, or
    using a string representation of a numeric address. In the case of
    gethostbyaddr(), the host is specified using a
    binary representation 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 consisting 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 corresponding to the value of the
    err parameter.
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_FOUNDTRY_AGAINNO_RECOVERYNO_DATAherror() function appeared in
  4.3BSD. The endhostent(),
  gethostbyaddr(),
  gethostbyname(), gethostent(),
  and sethostent() functions appeared in
  4.2BSD. The gethostbyname2()
  function first appeared in bind-4.9.4. IPv6 support was implemented in WIDE
  Hydrangea IPv6 protocol stack kit.
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.
The gethostent() does not currently follow
    the search order specified in
    nsswitch.conf(5) and
    only reads the /etc/hosts file.
| August 19, 2013 | NetBSD 9.3 |