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## Copyright (C) 2010-2013 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} is_valid_file_id (@var{fid})
## Return true if @var{fid} refers to an open file.
## @seealso{fopen}
## @end deftypefn
function retval = is_valid_file_id (fid)
retval = false;
if (nargin == 1)
try
if (isscalar (fid))
[file, mode, arch] = fopen (fid);
retval = ! isempty (file);
endif
end_try_catch
else
print_usage ();
endif
endfunction
%!assert (is_valid_file_id (stdout))
%!assert (! is_valid_file_id ([1,2;3,4]))
%!assert (! is_valid_file_id ("not_a_file_id"))
%!assert (! is_valid_file_id (-1))
%!assert (! is_valid_file_id (pi))
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