为 C++ function 编写 GNU Octave 包装器

Question

I'm trying to edit an GNU Octave wrapper for a C++ function to use it with raspberry pi. I have zero experience with C++ or Octave prior to this (have experience with python and matlab) so I am struggling a little on understanding how this works.

Someone has already written a partial GNU Octave wrapper for a C++ function library as you see here

What I am trying to do is to add additional functions to this wrapper. For example, I would like to edit the block shown here:

DEFUN_DLD (bcm2835_gpio_fsel, args, nargout,
  "-*- texinfo -*-\n\
@deftypefn  {} bcm2835_gpio_fsel (@var{pin}, @var{mode})\n\
TDOD: document me!\n\
@end deftypefn")
{
  octave_value_list retval;
  int nargin = args.length ();

  if (nargin != 2)
    print_usage ();

  if (! init_ret)
    error ("bcm2835 not initialized");

  int pin = args(0).int_value();
  int mode = args(1).int_value();

  bcm2835_gpio_fsel (pin, mode);
  return retval;
}

The purpose is to allow the function bcm2835_gpio_fsel to be able to take a string input. (you can see here for the C++ library) I think the parts I need to change are probably int mode = args.int_value(); to something like string mode = args(1); .

There are several things that I am curious about:

1. Is my above thinking correct? (re: taking in string input vs int input)
2. What is the octave_value_list retval; that is written on the top of this code block? I read that "The return type of functions defined with DEFUN_DLD is always octave_value_list." but I'm not quite sure I understand what this means. So it seems like you are initializing a variable that's called retval with type octave_value_list. Is this some form of an array? Not sure...

Thanks a ton!

Answer 1

I will answer question 2 first:

2. What is the octave_value_list retval; that is written on the top of this code block? I read that "The return type of functions defined with DEFUN_DLD is always octave_value_list." but I'm not quite sure I understand what this means. So it seems like you are initializing a variable that's called retval with type octave_value_list. Is this some form of an array? Not sure...

The octave_value_list is a list of octave_value . An octave_value is a type that wraps anything that you will handle in the Octave interpreter (command-line interface). So, when in Octave you call:

[a, b] = foobar (x, y, z);

The function foobar will receive an octave_value_list with three elements ( octave_value ), and return an octave_value_list with two arguments.

When you call:

a = foobar (x);

Then the function will still receive and return octave_value_list s, each with one element.

If you're not looking at the Octave C++ headers, then the best alternative is to look at Octave's doxygen documentation . There, you can get an almost complete list of methods for octave_value .

Now, it's easier to answer your first question:

1. Is my above thinking correct? (re: taking in string input vs int input)

Kind of. You're right in that you can get a string from an argument but you're doing it wrong. string mode = args(1); will fail because args(1) returns an octave_value . Instead, you need to do std::string mode = args(1).string_value();