From bug-octave-request at bevo dot che dot wisc dot edu  Wed Nov 19 00:19:46 1997
Subject: Initial value of global variable
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Maximilian Pitschi <Maximilian dot Pitschi at ofw dot pr dot siemens dot de>
cc: bug-octave at bevo dot che dot wisc dot edu
Date: Wed, 19 Nov 1997 00:17:22 -0600

On 18-Nov-1997, Maximilian Pitschi <Maximilian dot Pitschi at ofw dot pr dot siemens dot de> wrote:

| In matlab, the initial value of a global variable
| is the empty matrix, [].  In octave (with --traditional), such a
| variable is not defined.

Here is a patch to try.  It should initialize global variables to the
empty matrix, along with making statements like

  global foo = initial_foo_value;

only perform the assignment if the global foo does not already have a
value.  Some of the M-files distributed with Octave will also need
to be changed, but the patch below does not fix them.  They will be
updated before the next test release (coming soon).

Thanks,

jwe

Tue Nov 18 04:27:55 1997  John W. Eaton  <jwe at bevo dot che dot wisc dot edu>

	* pt-misc.cc (tree_global::eval): Initialize global values to `[]'.
	Only perform explicit initialization once.


*** src/pt-misc.cc~	Fri Feb 28 15:23:32 1997
--- src/pt-misc.cc	Tue Nov 18 23:55:07 1997
***************
*** 441,446 ****
--- 441,451 ----
    if (id)
      {
        id->link_to_global ();
+ 
+       octave_value tmp = id->value ();
+ 
+       if (tmp.is_undefined ())
+ 	id->define (new tree_constant (Matrix ()));
      }
    else if (ass_expr)
      {
***************
*** 450,456 ****
  	  && (idnt = ass_expr->left_hand_side_id ()))
  	{
  	  idnt->link_to_global ();
! 	  ass_expr->eval (false);
  	}
        else
  	error ("global: unable to make individual structure elements global");
--- 455,468 ----
  	  && (idnt = ass_expr->left_hand_side_id ()))
  	{
  	  idnt->link_to_global ();
! 
! 	  // Only perform assignment if the global symbol doesn't
! 	  // already have a value as a variable.
! 
! 	  octave_value tmp = idnt->value ();
! 
! 	  if (tmp.is_undefined ())
! 	    ass_expr->eval (false);
  	}
        else
  	error ("global: unable to make individual structure elements global");