From bug-octave-request at bevo dot che dot wisc dot edu Wed Sep 18 02:22:54 2002
Subject: Bug in octave structures
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Roderick Koehle <roderick dot koehle at web dot de>
Cc: bug-octave at bevo dot che dot wisc dot edu, octave-maintainers@bevo.che.wisc.edu
Date: Wed, 18 Sep 2002 02:22:01 -0500

On 17-Sep-2002, Roderick Koehle <roderick dot koehle at web dot de> wrote:

| In the current octave CVS release, I discovered following problems:
| 
| octave:1> z = zeros(1,5);
| octave:2> s.a = z; s.b = z; s.a(1) = 1; s
| s =
| {
|   a =
| 
|     1  0  0  0  0
| 
|   b =
| 
|     1  0  0  0  0
| 
| }
| It seems that by assigning the vector z to s.a and s.b, these variables stay 
| linked forever. Whatever you write into the vector s.a will also modify s.b.
| 
| Doing the same with scalar values however works properly. So the example:
| 
| octave:1> z = 0;  s.a = z; s.b = z; s.a(1) = 1; s
| s =
| {
|   a = 1
|   b = 0
| }
| 
| So for the scalar case, above example produces the correct result, writing 
| into a does not cause b to be modified.
| 
| The following example produces also curious results.
| A function "empty" returns a structure with an empty list element.
| When you write something into this list and then try to clear it again with 
| the function "empty", you will get following:
| 
| octave:1> function a=empty(), a.list = {}; endfunction
| octave:2> a=empty() 
| a =
| {
|   list = {}
| }
| 
| octave:3> a.list{1} = 'hallo'
| a.list =
| {
|   list =
|   {
|     [1,1] = hallo
|   }
| }
| 
| octave:4> a = empty()
| a =
| {
|   list =
|   {
|     [1,1] = hallo
|   }
| }
| 
| Even though in the function "empty" the empty list is assigned to a.list. It 
| won't change its content.

Please try the following patch.  It's checked in to CVS now too, so
you could also update to get these changes.

Thanks,

jwe


2002-09-18  John W. Eaton  <jwe at bevo dot che dot wisc dot edu>

	* ov-struct.cc (octave_struct::subsasgn): Ensure that indexed
	object is not shared before calling subsasgn.


Index: ov-struct.cc
===================================================================
RCS file: /usr/local/cvsroot/octave/src/ov-struct.cc,v
retrieving revision 1.22
diff -u -r1.22 ov-struct.cc
--- ov-struct.cc	3 Jun 2002 18:15:47 -0000	1.22
+++ ov-struct.cc	18 Sep 2002 07:19:16 -0000
 at @ -239,6 +239,8 @@
 			next_idx.remove_front ();
 			next_idx.remove_front ();
 
+			u.make_unique ();
+
 			t_rhs = u.subsasgn (type.substr (2), next_idx, rhs);
 		      }
 		  }
 at @ -274,6 +276,8 @@
 		SLList<octave_value_list> next_idx (idx);
 
 		next_idx.remove_front ();
+
+		u.make_unique ();
 
 		t_rhs = u.subsasgn (type.substr (1), next_idx, rhs);
 	      }



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