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A.3 Standalone Programs

The libraries Octave itself uses can be utilized in standalone applications. These applications then have access, for example, to the array and matrix classes, as well as to all of the Octave algorithms. The following C++ program, uses class Matrix from liboctave.a or liboctave.so.

#include <iostream>
#include <octave/oct.h>

int
main (void)
{
  std::cout << "Hello Octave world!\n";

  int n = 2;
  Matrix a_matrix = Matrix (n, n);

  for (octave_idx_type i = 0; i < n; i++)
    for (octave_idx_type j = 0; j < n; j++)
      a_matrix(i,j) = (i + 1) * 10 + (j + 1);

  std::cout << a_matrix;

  return 0;
}

mkoctfile can be used to build a standalone application with a command like

$ mkoctfile --link-stand-alone standalone.cc -o standalone
$ ./standalone
Hello Octave world!
  11 12
  21 22
$

Note that the application standalone will be dynamically linked against the Octave libraries and any Octave support libraries. The above allows the Octave math libraries to be used by an application. It does not, however, allow the script files, oct-files, or builtin functions of Octave to be used by the application. To do that the Octave interpreter needs to be initialized first. An example of how to do this can then be seen in the code

#include <iostream>
#include <octave/oct.h>
#include <octave/octave.h>
#include <octave/parse.h>
#include <octave/toplev.h>

int
main (void)
{
  string_vector argv (2);
  argv(0) = "embedded";
  argv(1) = "-q";

  octave_main (2, argv.c_str_vec (), 1);

  octave_idx_type n = 2;
  octave_value_list in;

  for (octave_idx_type i = 0; i < n; i++)
    in(i) = octave_value (5 * (i + 2));

  octave_value_list out = feval ("gcd", in, 1);

  if (! error_state && out.length () > 0)
    std::cout << "GCD of ["
              << in(0).int_value ()
              << ", "
              << in(1).int_value ()
              << "] is " << out(0).int_value ()
              << std::endl;
  else
    std::cout << "invalid\n";

  clean_up_and_exit (0);
}

which, as before, is compiled and run as a standalone application with

$ mkoctfile --link-stand-alone embedded.cc -o embedded
$ ./embedded
GCD of [10, 15] is 5
$

It is worth noting that, if only builtin functions are to be called from a C++ standalone program, then it does not need to initialize the interpreter to do so. The general rule is that, for a builtin function named function_name in the interpreter, there will be a C++ function named Ffunction_name (note the prepended capital F) accessible in the C++ API. The declarations for all builtin functions are collected in the header file builtin-defun-decls.h. This feature should be used with care as the list of built-in functions can change. No guarantees can be made that a function that is currently built in won’t be implemented as a .m file or as a dynamically linked function in the future. An example of how to call builtin functions from C++ can be seen in the code

#include <iostream>
#include <octave/oct.h>
#include <octave/builtin-defun-decls.h>

int
main (void)
{

  int n = 2;
  Matrix a_matrix = Matrix (n, n);

  for (octave_idx_type i = 0; i < n; i++)
    for (octave_idx_type j = 0; j < n; j++)
      a_matrix(i,j) = (i + 1) * 10 + (j + 1);

  std::cout << "This is a matrix:" 
            << std::endl 
            << a_matrix
            << std::endl;

  octave_value_list in;
  in(0) = a_matrix;

  octave_value_list out = Fnorm (in, 1);
  double norm_of_the_matrix = out(0).double_value ();

  std::cout << "This is the norm of the matrix:" 
            << std::endl 
            << norm_of_the_matrix
            << std::endl;
  
  return 0;
}

which, again, is compiled and run as a standalone application with

$ mkoctfile --link-stand-alone standalonebuiltin.cc -o standalonebuiltin
$ ./standalonebuiltin 
This is a matrix:
 11 12
 21 22

This is the norm of the matrix:
34.4952


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