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There is often a need to be able to call another octave function from
within an oct-file, and there are many examples of such within octave
itself. For example the quad
function is an oct-file that
calculates the definite integral by quadrature over a user supplied
function.
There are also many ways in which a function might be passed. It might be passed as one of
The example below demonstrates an example that accepts all four means of passing a function to an oct-file.
/* 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/parse.h> DEFUN_DLD (funcdemo, args, nargout, "Function Demo") { int nargin = args.length(); octave_value_list retval; if (nargin < 2) print_usage (); else { octave_value_list newargs; for (octave_idx_type i = nargin - 1; i > 0; i--) newargs (i - 1) = args(i); if (args(0).is_function_handle () || args(0).is_inline_function ()) { octave_function *fcn = args(0).function_value (); if (! error_state) retval = feval (fcn, newargs, nargout); } else if (args(0).is_string ()) { std::string fcn = args (0).string_value (); if (! error_state) retval = feval (fcn, newargs, nargout); } else error ("funcdemo: expected string,", " inline or function handle"); } return retval; }
The first argument to this demonstration is the user supplied function and the following arguments are all passed to the user function.
funcdemo (@sin,1) 0.84147 funcdemo (@(x) sin(x), 1) 0.84147 funcdemo (inline ("sin(x)"), 1) 0.84147 funcdemo ("sin",1) 0.84147 funcdemo (@atan2, 1, 1) 0.78540
When the user function is passed as a string, the treatment of the
function is different. In some cases it is necessary to always have the
user supplied function as an octave_function
object. In that
case the string argument can be used to create a temporary function like
std::octave fcn_name = unique_symbol_name ("__fcn__"); std::string fname = "function y = "; fname.append (fcn_name); fname.append ("(x) y = "); fcn = extract_function (args(0), "funcdemo", fcn_name, fname, "; endfunction"); ... if (fcn_name.length ()) clear_function (fcn_name);
There are two important things to know in this case. The number of input arguments to the user function is fixed, and in the above is a single argument, and secondly to avoid leaving the temporary function in the Octave symbol table it should be cleared after use.