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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")
      {
        if (args.length () != 1)
          print_usage ();
      
        octave_value retval;
      
        std::string s = args(0).string_value ();
      
        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
 

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