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>GETHOSTBYNAME(3)        System Library Functions Manual       GETHOSTBYNAME(3)
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NAME
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     gethostbyname, gethostbyname2, gethostbyaddr, gethostent, sethostent,
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     endhostent, hstrerror, herror - get network host entry
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SYNOPSIS
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     #include &lt;netdb.h&#62;
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     extern int h_errno;
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     struct hostent *
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     gethostbyname(const char *name);
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     struct hostent *
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     gethostbyname2(const char *name, int af);
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     struct hostent *
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     gethostbyaddr(const char *addr, int len, int af);
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     struct hostent *
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     gethostent(void);
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     void
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     sethostent(int stayopen);
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     void
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     endhostent(void);
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     void
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     herror(const char *string);
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     const char *
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     hstrerror(int err);
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DESCRIPTION
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     The gethostbyname() and gethostbyaddr() functions each return a pointer
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     to an object with the following structure describing an internet host
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     referenced by name or by address, respectively.  This structure contains
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     either information obtained from the name server (i.e., resolver(3) and
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     named(8)), broken-out fields from a line in /etc/hosts, or database
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     entries supplied by the yp(8) system.  resolv.conf(5) describes how the
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     particular database is chosen.
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     struct  hostent {
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             char    *h_name;        /* official name of host */
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             char    **h_aliases;    /* alias list */
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             int     h_addrtype;     /* host address type */
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             int     h_length;       /* length of address */
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             char    **h_addr_list;  /* list of addresses from name server */
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     };
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     #define h_addr  h_addr_list[0]  /* address, for backward compatibility */
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     The members of this structure are:
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     h_name       Official name of the host.
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     h_aliases    A zero-terminated array of alternate names for the host.
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     h_addrtype   The type of address being returned.
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     h_length     The length, in bytes, of the address.
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     h_addr_list  A zero-terminated array of network addresses for the host.
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                  Host addresses are returned in network byte order.
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     h_addr       The first address in h_addr_list; this is for backward com-
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                  patibility.
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     The function gethostbyname() will search for the named host in the cur-
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     rent domain and its parents using the search lookup semantics detailed in
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     resolv.conf(5) and hostname(7).
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     gethostbyname2() is an advanced form of gethostbyname() which allows
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     lookups in address families other than AF_INET, for example AF_INET6.
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     The gethostbyaddr() function will search for the specified address of
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     length len in the address family af.  The only address family currently
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     supported is AF_INET.
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     The sethostent() function may be used to request the use of a connected
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     TCP socket for queries.  If the stayopen flag is non-zero, this sets the
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     option to send all queries to the name server using TCP and to retain the
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     connection after each call to gethostbyname() or gethostbyaddr().  Other-
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     wise, queries are performed using UDP datagrams.
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     The endhostent() function closes the TCP connection.
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     The herror() function prints an error message describing the failure.  If
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     its argument string is non-null, it is prepended to the message string
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     and separated from it by a colon (`:') and a space.  The error message is
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     printed with a trailing newline.  The contents of the error message is
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     the same as that returned by hstrerror() with argument h_errno.
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FILES
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     /etc/hosts
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     /etc/resolv.conf
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DIAGNOSTICS
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     Error return status from gethostbyname(), gethostbyname2(), and
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     gethostbyaddr() is indicated by return of a null pointer.  The external
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     integer h_errno may then be checked to see whether this is a temporary
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     failure or an invalid or unknown host.
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     The variable h_errno can have the following values:
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     HOST_NOT_FOUND  No such host is known.
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     TRY_AGAIN       This is usually a temporary error and means that the
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                     local server did not receive a response from an authori-
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                     tative server.  A retry at some later time may succeed.
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     NO_RECOVERY     Some unexpected server failure was encountered.  This is
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                     a non-recoverable error.
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     NO_DATA         The requested name is valid but does not have an IP
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                     address; this is not a temporary error.  This means that
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                     the name is known to the name server but there is no
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                     address associated with this name.  Another type of
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                     request to the name server using this domain name will
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                     result in an answer; for example, a mail-forwarder may be
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                     registered for this domain.
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SEE ALSO
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     resolver(3), getaddrinfo(3), getnameinfo(3), hosts(5), resolv.conf(5),
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     hostname(7), named(8)
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CAVEAT
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     If the search routines in resolv.conf(5) decide to read the /etc/hosts
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     file, gethostent() and other functions will read the next line of the
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     file, re-opening the file if necessary.
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     The sethostent() function opens and/or rewinds the file /etc/hosts.  If
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     the stayopen argument is non-zero, the file will not be closed after each
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     call to gethostbyname(), gethostbyname2(), or gethostbyaddr().
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     The endhostent() function closes the file.
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HISTORY
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     The herror() function appeared in 4.3BSD.  The endhostent(),
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     gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func-
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     tions appeared in 4.2BSD.
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BUGS
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     These functions use static data storage; if the data is needed for future
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     use, it should be copied before any subsequent calls overwrite it.  Only
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     the Internet address formats are currently understood.
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     YP does not support any address families other than AF_INET and uses the
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     traditional database format.
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BSD                             March 13, 1997                             BSD
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