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.\"
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.\" Copyright 1998 by the Massachusetts Institute of Technology.
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.\"
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.\" Permission to use, copy, modify, and distribute this
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.\" software and its documentation for any purpose and without
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.\" fee is hereby granted, provided that the above copyright
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.\" notice appear in all copies and that both that copyright
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.\" notice and this permission notice appear in supporting
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.\" documentation, and that the name of M.I.T. not be used in
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.\" advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission.
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.\" M.I.T. makes no representations about the suitability of
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.\" this software for any purpose. It is provided "as is"
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.\" without express or implied warranty.
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.\"
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.TH ARES_GETHOSTBYADDR 3 "24 July 1998"
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.SH NAME
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ares_gethostbyaddr \- Initiate a host query by address
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.SH SYNOPSIS
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.nf
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#include <ares.h>
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typedef void (*ares_host_callback)(void *\fIarg\fP, int \fIstatus\fP,
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int \fItimeouts\fP,
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struct hostent *\fIhostent\fP)
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void ares_gethostbyaddr(ares_channel \fIchannel\fP, const void *\fIaddr\fP,
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int \fIaddrlen\fP, int \fIfamily\fP,
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ares_host_callback \fIcallback\fP, void *\fIarg\fP)
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.fi
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.SH DESCRIPTION
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The
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.B ares_gethostbyaddr
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function initiates a host query by address on the name service channel
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identified by
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.IR channel .
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The parameters
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.I addr
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and
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.I addrlen
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give the address as a series of bytes, and
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.I family
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gives the type of address. When the query is complete or has failed, the ares
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library will invoke \fIcallback\fP. Completion or failure of the query may
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happen immediately, or may happen during a later call to
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\fIares_process(3)\fP, \fIares_destroy(3)\fP or \fIares_cancel(3)\fP.
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.PP
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The callback argument
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.I arg
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is copied from the
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.B ares_gethostbyaddr
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argument
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.IR arg .
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The callback argument
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.I status
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indicates whether the query succeeded and, if not, how it failed. It
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may have any of the following values:
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.TP 19
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.B ARES_SUCCESS
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The host lookup completed successfully.
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.TP 19
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.B ARES_ENOTIMP
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The ares library does not know how to look up addresses of type
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.IR family .
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.TP 19
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.B ARES_ENOTFOUND
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The address
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.I addr
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was not found.
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.TP 19
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.B ARES_ENOMEM
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Memory was exhausted.
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.TP 19
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.B ARES_ECANCELLED
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The query was cancelled.
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.TP 19
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.B ARES_EDESTRUCTION
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The name service channel
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.I channel
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is being destroyed; the query will not be completed.
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.PP
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The callback argument
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.I timeouts
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reports how many times a query timed out during the execution of the
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given request.
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.PP
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On successful completion of the query, the callback argument
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.I hostent
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points to a
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.B struct hostent
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containing the name of the host returned by the query. The callback
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need not and should not attempt to free the memory pointed to by
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.IR hostent ;
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the ares library will free it when the callback returns. If the query
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did not complete successfully,
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.I hostent
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will be
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.BR NULL .
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.SH SEE ALSO
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.BR ares_process (3),
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.BR ares_gethostbyname (3)
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.SH AUTHOR
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Greg Hudson, MIT Information Systems
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.br
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Copyright 1998 by the Massachusetts Institute of Technology.
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