how to call an octave .m file from a C++ program

[vermeij]

Hi,

I tried to find information on how to call an octave .m file from a  
C++ program. There is some information around, but most of it is no  
longer up-to-date, it was not trivial to get it working. In this post  
I want to explain how to do it, maybe it is useful to somebody.

I have a file called exampleOctaveFunction.m which looks like this:

-------------------------------------
function [resultScalar, resultString, resultMatrix] =  
exampleOctaveFunction (inScalar, inString, inMatrix)

  resultScalar = (inScalar * pi);
  resultString = strcat ('Good morning Mr. ', inString);
  resultMatrix = (inMatrix + 1);

endfunction
-------------------------------------

I have a file called how-to-call-octave.cpp which is this:

-------------------------------------
#include <octave/oct.h>
#include <octave/octave.h>
#include <octave/parse.h>
#include <octave/toplev.h> /* do_octave_atexit */

int main (const int argc, char ** argv)
{
  const char * argvv [] = {"" /* name of program, not relevant */,  
"--silent"};

  octave_main (2, (char **) argvv, true /* embedded */);

  octave_value_list functionArguments;

  functionArguments (0) = 2;
  functionArguments (1) = "D. Humble";

  Matrix inMatrix (2, 3);

  inMatrix (0, 0) = 10;
  inMatrix (0, 1) = 9;
  inMatrix (0, 2) = 8;
  inMatrix (1, 0) = 7;
  inMatrix (1, 1) = 6;
  functionArguments (2) = inMatrix;

  const octave_value_list result = feval ("exampleOctaveFunction",  
functionArguments, 1);

  std::cout << "resultScalar is " << result (0).scalar_value () << std::endl;
  std::cout << "resultString is " << result (1).string_value () << std::endl;
  std::cout << "resultMatrix is\n" << result (2).matrix_value ();

  do_octave_atexit ();
}
-------------------------------------

And a little readme file, called readme.sh, that explains how to  
compile and run this simple example:

-------------------------------------
#! /bin/bash

#
# Make sure you have octave installed. On my system, Ubuntu 8.10, I installed
# the packages octave3.0 and octave3.0-headers.
#
# To compile, type
#
make how-to-call-octave.o
#
# which, on my system, is equivalent to
#
#   g++ -c -o how-to-call-octave.o how-to-call-octave.cpp
#
# To link, type
#
g++ -L /usr/lib/octave-3.0.1/ -l octinterp -o how-to-call-octave  
how-to-call-octave.o
#
# Adjust the directory in the -L directive according to the configuration of
# your machine.
#
# To run, type
#
./how-to-call-octave
#
# It should output something like
#
#   resultScalar is 6.28319
#   resultString is Good morning Mr. D. Humble
#   resultMatrix is
#    11 10 9
#    8 7 1
#
# Hope this is of help to somebody.
#
-------------------------------------

You can also execute the readme.sh file and it will compile and run for you.

Good luck, Arjan.
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