.\" $Id$
.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
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.\" software and its documentation for any purpose and without
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.TH ARES_GETHOSTBYADDR 3 "24 July 1998"
.SH NAME
ares_gethostbyaddr \- Initiate a host query by address
.SH SYNOPSIS
.nf
.B #include <ares.h>
.PP
.B typedef void (*ares_host_callback)(void *\fIarg\fP, int \fIstatus\fP,
.B	struct hostent *\fIhostent\fP)
.PP
.B void ares_gethostbyaddr(ares_channel \fIchannel\fP, const void *\fIaddr\fP,
.B 	int \fIaddrlen\fP, int \fIfamily\fP, ares_host_callback \fIcallback\fP,
.B 	void *\fIarg\fP)
.fi
.SH DESCRIPTION
The
.B ares_gethostbyaddr
function initiates a host query by address on the name service channel
identified by
.IR channel .
The parameters
.I addr
and
.I addrlen
give the address as a series of bytes, and
.I family
gives the type of address.  When the query is complete or has failed,
the ares library will invoke
.IR callback .
Completion or failure of the query may happen immediately, or may
happen during a later call to
.BR ares_process (3)
or
.BR ares_destroy (3).
.PP
The callback argument
.I arg
is copied from the
.B ares_gethostbyaddr
argument
.IR arg .
The callback argument
.I status
indicates whether the query succeeded and, if not, how it failed.  It
may have any of the following values:
.TP 19
.B ARES_SUCCESS
The host lookup completed successfully.
.TP 19
.B ARES_ENOTIMP
The ares library does not know how to look up addresses of type
.IR family .
.TP 19
.B ARES_ENOTFOUND
The address
.I addr
was not found.
.TP 19
.B ARES_ENOMEM
Memory was exhausted.
.TP 19
.B ARES_EDESTRUCTION
The name service channel
.I channel
is being destroyed; the query will not be completed.
.PP
On successful completion of the query, the callback argument
.I hostent
points to a
.B struct hostent
containing the name of the host returned by the query.  The callback
need not and should not attempt to free the memory pointed to by
.IR hostent ;
the ares library will free it when the callback returns.  If the query
did not complete successfully,
.I hostent
will be
.BR NULL .
.SH SEE ALSO
.BR ares_process (3)
.SH AUTHOR
Greg Hudson, MIT Information Systems
.br
Copyright 1998 by the Massachusetts Institute of Technology.