### 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 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 then 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 `hello` 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>

         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;
           Matrix a_matrix = Matrix (1, 2);

           std::cout << "GCD of [";
           for (octave_idx_type i = 0; i < n; i++)
             {
               a_matrix (i) = 5 * (i + 1);
               if (i != 0)
                 std::cout << ", " << 5 * (i + 2);
               else
                 std::cout << 5 * (i + 2);
             }
           std::cout << "] is ";

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

           if (!error_state && out.length () > 0)
             {
               a_matrix = out(0).matrix_value ();
               if (a_matrix.numel () == 1)
                 std::cout << a_matrix(0) << "\n";
               else
                 std::cout << "invalid\n";
             }
           else
             std::cout << "invalid\n";

           return 0;
         }

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

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