doubts about functions declared in parse.h ...

[John W. Eaton]

On 11-Mar-2005, Alberto Francisco Martin Huertas <address@hidden> wrote:

| Hello. I'm a spanish university student and I'm performing my final career
| project with Octave. I'm developing a DLF (Dinamycally Loaded Function) for
| Octave, and  I'm interested in to know if there is any function declared in
| parse.h header file that allows you to parse and execute some octave script
| file without modifying some other enviroment variables used before. For
| example, if the following script file (called example.m) had the following
| sentence:
| 
|     A=3;
|  
| and my DLD function were something like this:
| 
|       DEFUN_DLD(example_function, arguments, ,
|           "a example function") { 
|                 the_function_im_looking_for("example.m");
|                 return eval_string("A",...); 
|                 
| 
|      } 
| 
| I would like the following behaviour in a Octave session:
| 
| octave:1> A=1
| A = 1
| octave:2> example_function()
| ans = 3
| octave:2> A
| A = 1

The following will do what you want, but why do you want this
behavior?  What are you really trying to do?

#include <octave/oct.h>
#include <octave/parse.h>

DEFUN_DLD (exfun, args, , "exfun (file, sym)")
{
  octave_value_list retval;

  if (args.length () == 2)
    {
      std::string fname = args(0).string_value ();
      std::string sym = args(1).string_value ();

      if (! error_state)
        {
          source_file (fname);

          if (! error_state)
            {
              symbol_record *sr = curr_sym_tab->lookup (sym);

              if (sr)
                retval(0) = sr->def ();
              else
                error ("exfun: symbol \"%s\" not found", sym.c_str ());
            }
        }
    }
  else
    print_usage ("exfun");

  return retval;
}

Example of using this:

  $ cat script.m
  a = 2;

  octave:1> exfun ("script.m", "a")
  ans = 2
  octave:2> a
  a = 2


Note that the seemingly equivalent function

  function retval = exfun (file, sym)
    if (nargin == 2)
      source (file);
      retval = eval (sym);
    else
      usage ("exfun (file, sym)");
    endif
  endfunction

does not work, because functions like this introduce a local scope and
C++ functions do not.  This is normally not a source of confusion,
because it is not common to source a file inside a C++ function.

jwe



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