How to instantiate an Octave classdef object in C++ and call its methods

Question

I know how to call a function defined in an .m-file using the Octave interpreter and feval as shown in the Octave manual but not how to do something similar using Octave classes and their methods.

If I have a simple class defined in Octave using the classdef method such as

classdef TestClass < handle
  properties
    val
  endproperties
  methods
    function obj = TestClass()
      obj.val = 1;
    endfunction 
    function obj = setval(obj, v)
      obj.val = v;
    endfunction
    function showval(obj)
      disp(obj.val);
    endfunction  
  endmethods
endclassdef

If I then would would like to use my class in some C++ code, how would I go about doing that. In Octave it would be:

c = TestClass(); //create an instance of TestClass
c.setval(100); //use the objects methods
c.showval(); //display 100

Solution

Based on the answer below I'll present my solution here. The above octave code can be rewritten as

c = TestClass();
setval(c, 100);
showval(c);

which can be turned into this C++ code

#include <interpreter.h>
#include <parse.h>

int main()
{
    octave::interpreter interpreter;
    interpreter.execute();

    octave_value_list arg;
    octave_value c;
    
    c = octave::feval("TestClass", arg, 1).xelem(0);     

    arg(0) = c; 
    arg(1) = 100;
    octave::feval("setval", arg);  

    arg.clear(); 
    arg(0) = c;
    octave::feval("showval", arg);  

    return 0;
}

Answer 1

If you already know how to call an Octave function from C++, then all you are missing is that a.b() is the same as b(a). Calling a method is just like calling a function, there is no distinction. Octave figures out which overload of the function to call based on the input arguments.

The bit of Octave code you posted,

c = TestClass();
c.setval(100);
c.showval();

can also be written as

c = TestClass();
setval(c, 100);
showval(c);