GNU Octave: Accessing Global Variables in Oct-Files

A.1.7 Accessing Global Variables in Oct-Files

Global variables allow variables in the global scope to be accessed. Global variables can be accessed within oct-files by using the support functions get_global_value and set_global_value. get_global_value takes two arguments, the first is a string representing the variable name to obtain. The second argument is a boolean argument specifying what to do if no global variable of the desired name is found. An example of the use of these two functions is

#include <octave/oct.h>

DEFUN_DLD (globaldemo, args, , "Global Demo")
{
  octave_value retval;
  int nargin = args.length ();

  if (nargin != 1)
    print_usage ();
  else
    {
      std::string s = args(0).string_value ();
      if (! error_state)
        {
          octave_value tmp = get_global_value (s, true);
          if (tmp.is_defined ())
            retval = tmp;
          else
            retval = "Global variable not found";

          set_global_value ("a", 42.0);
        }
    }
  return retval;
}

An example of its use is

global a b
b = 10;
globaldemo ("b")
⇒ 10
globaldemo ("c")
⇒ "Global variable not found"
num2str (a)
⇒ 42