Unix/Linux Go Back    

RedHat 9 (Linux i386) - man page for gethostbyname2 (redhat section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)

GETHOSTBYNAME(3)		    Linux Programmer's Manual			 GETHOSTBYNAME(3)

       gethostbyname, gethostbyaddr, sethostent, endhostent, herror, hstrerror - get network host

       #include <netdb.h>
       extern int h_errno;

       struct hostent *gethostbyname(const char *name);

       #include <sys/socket.h>	      /* for AF_INET */
       struct hostent *gethostbyaddr(const char *addr,
	 int len, int type);

       void sethostent(int stayopen);

       void endhostent(void);

       void herror(const char *s);

       const char *hstrerror(int err);

       /* GNU extensions */
       struct hostent *gethostbyname2(const char *name, int af);

       int gethostbyname_r (const char *name,
	 struct hostent *ret, char *buf, size_t buflen,
	 struct hostent **result, int *h_errnop);

       int gethostbyname2_r (const char *name, int af,
	 struct hostent *ret, char *buf, size_t buflen,
	 struct hostent **result, int *h_errnop);

       The gethostbyname() function returns a structure of type hostent for the given host  name.
       Here  name  is either a host name, or an IPv4 address in standard dot notation, or an IPv6
       address in colon (and possibly dot) notation. (See RFC 1884 for the  description  of  IPv6
       addresses.)   If  name  is  an IPv4 or IPv6 address, no lookup is performed and gethostby-
       name() simply copies name into the h_name field and its struct in_addr equivalent into the
       h_addr_list[0]  field of the returned hostent structure.  If name doesn't end in a dot and
       the environment variable HOSTALIASES is set, the alias file pointed to by HOSTALIASES will
       first  be searched for name (see hostname(7) for the file format).  The current domain and
       its parents are searched unless name ends in a dot.

       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 dur-
       ing 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 (obsolete) herror() function prints the error  message  associated  with  the  current
       value of h_errno on stderr.

       The  (obsolete) hstrerror() function takes an error number (typically h_errno) and returns
       the corresponding message string.

       The domain name queries carried out by gethostbyname() and gethostbyaddr() use a  combina-
       tion 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

       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.

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

	      The type of address; always AF_INET at present.

	      The length of the address in bytes.

	      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 compatibility.

       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.

       The variable h_errno can have the following values:

	      The specified host is unknown.

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

	      A non-recoverable name server error occurred.

	      A temporary error occurred on an authoritative name server.  Try again later.

	      resolver configuration file

	      host database file

       BSD 4.3.

       The  SUS-v2  standard  is buggy and declares the len parameter of gethostbyaddr() to be of
       type size_t.  (That is wrong, because  it  has  to  be  int,  and  size_t  is  not.  POSIX
       1003.1-2001 makes it socklen_t, which is OK.)

       The  functions  gethostbyname()	and  gethostbyaddr()  may return pointers to static data,
       which may be overwritten by later calls. Copying the  struct  hostent  does  not  suffice,
       since it contains pointers - a deep copy is required.

       Glibc2 also has a gethostbyname2() that works like gethostbyname(), but permits to specify
       the address family to which the address must belong.

       Glibc2 also has reentrant versions gethostbyname_r() and gethostbyname2_r().  These return
       0 on success and nonzero on error. The result of the call is now stored in the struct with
       address ret.  After the call, *result will be NULL on error or point to the result on suc-
       cess.  Auxiliary data is stored in the buffer buf of length buflen.  (If the buffer is too
       small, these functions will return ERANGE.)  No global variable h_errno is  modified,  but
       the address of a variable in which to store error numbers is passed in h_errnop.

       POSIX 1003.1-2001 marks gethostbyaddr() and gethostbyname() legacy, and introduces

       struct hostent *getipnodebyaddr (const void *restrict addr,
	 socklen_t len, int type, int *restrict error_num);

       struct hostent *getipnodebyname (const char *name,
	 int type, int flags, int *error_num);

       resolver(3), hosts(5), hostname(7), resolv+(8), named(8)

BSD					    2000-08-12				 GETHOSTBYNAME(3)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums

All times are GMT -4. The time now is 12:15 AM.