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A structure in Octave is map between a number of fields represented and
their values. The Standard Template Library map
class is used,
with the pair consisting of a std::string
and an octave
Cell
variable.
A simple example demonstrating the use of structures within oct-files is
/* Copyright (C) 2006, 2007 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/>. */ #include <octave/oct.h> #include <octave/ov-struct.h> DEFUN_DLD (structdemo, args, , "Struct demo.") { int nargin = args.length (); octave_value retval; if (nargin != 2) print_usage (); else { Octave_map arg0 = args(0).map_value (); std::string arg1 = args(1).string_value (); if (! error_state && arg0.contains (arg1)) { // The following two lines might be written as // octave_value tmp; // for (Octave_map::iterator p0 = // arg0.begin(); // p0 != arg0.end(); p0++ ) // if (arg0.key (p0) == arg1) // { // tmp = arg0.contents (p0) (0); // break; // } // though using seek is more concise. Octave_map::const_iterator p1 = arg0.seek (arg1); octave_value tmp = arg0.contents(p1)(0); Octave_map st; st.assign ("selected", tmp); retval = octave_value (st); } } return retval; }
An example of its use is
x.a = 1; x.b = "test"; x.c = [1, 2]; structdemo (x, "b") => selected = test
The commented code above demonstrates how to iterate over all of the fields of the structure, where as the following code demonstrates finding a particular field in a more concise manner.
As can be seen the contents
method of the Octave_map
class
returns a Cell
which allows structure arrays to be represented.
Therefore, to obtain the underlying octave_value
we write
octave_value tmp = arg0.contents (p1) (0);
where the trailing (0) is the () operator on the Cell
object. We
can equally iterate of the elements of the Cell array to address the
elements of the structure array.