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GETHOSTBYNAME(3)       FreeBSD Library Functions Manual	      GETHOSTBYNAME(3)

NAME
     gethostbyname, gethostbyname2, 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 *
     gethostbyname2(const char *name, int af);

     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(), gethostbyname2() 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), 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 NULL-terminated array of alternate names for the host.

     h_addrtype	  The type of address being returned; usually 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()	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 environ-
     ment 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	for-
     mat.

     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
     else the function will return NULL	after having set h_errno to
     NETDB_INTERNAL

     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 consist-
     ing 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 cor-
     responding	to the value of	the err	parameter.

FILES
     /etc/hosts
     /etc/host.conf
     /etc/resolv.conf

DIAGNOSTICS
     Error return status from 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_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 authori-
		     tative 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.

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

CAVEAT
     The gethostent() function is defined, and sethostent() and	endhostent()
     are redefined, when libc(3) 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(), gethostbyname2() 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.	The gethostbyname2() function first appeared
     in	BIND version 4.9.4.

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.

FreeBSD	10.1			 May 25, 1995			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | CAVEAT | HISTORY | BUGS

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