.\" Copyright (c) 1999 Brian Somers <brian@Awfulhak.org>
.\" All rights reserved.
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.\" $FreeBSD: src/lib/libutil/realhostname.3,v 1.10 2005/02/13 22:25:14 ru Exp $
.\"
.Dd April 6, 1999
.Os
.Dt REALHOSTNAME 3
.Sh NAME
.Nm realhostname
.Nd "convert an IP number to the real host name"
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/types.h
.In netinet/in.h
.In libutil.h
.Ft int
.Fn realhostname "char *host" "size_t hsize" "const struct in_addr *ip"
.Sh DESCRIPTION
The function
.Fn realhostname
converts
.Ar ip
to the corresponding host name.
This is done by resolving
.Ar ip
to a host name and then ensuring that the host name resolves
back to
.Ar ip .
.Pp
.Ar host
must point to a buffer of at least
.Ar hsize
bytes, and will always be written to by this function.
.Pp
If the name resolution does not work both ways or if the host name is longer
than
.Ar hsize
bytes,
.Xr inet_ntoa 3
is used to convert
.Ar ip
to an ASCII form.
.Pp
If the string written to
.Ar host
is
.Ar hsize
bytes long,
.Ar host
will not be NUL terminated.
.Sh RETURN VALUES
The
.Fn realhostname
function will return one of the following constants which are defined in
.In libutil.h :
.Pp
.Bl -tag -width XXX -offset XXX
.It Li HOSTNAME_FOUND
A valid host name was found.
.It Li HOSTNAME_INCORRECTNAME
A host name was found, but it did not resolve back to the passed
.Ar ip .
.Ar host
now contains the numeric value of
.Ar ip .
.It Li HOSTNAME_INVALIDADDR
.Ar ip
could not be resolved.
.Ar host
now contains the numeric value of
.Ar ip .
.It Li HOSTNAME_INVALIDNAME
A host name was found, but it could not be resolved back to any ip number.
.Ar host
now contains the numeric value of
.Ar ip .
.El
.Sh SEE ALSO
.Xr gethostbyaddr 3 ,
.Xr gethostbyname 3 ,
.Xr inet_ntoa 3 ,
.Xr realhostname_sa 3