octave: Standalone Programs
A.3 Standalone Programs
=======================
The libraries Octave uses itself 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 built-in
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/interpreter.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 (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 re-iterating that, if only built-in functions are to be
called from a C++ standalone program then it does not need to initialize
the interpreter. The general rule is that for a built-in 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 built-in 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 a 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 built-in 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 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
$