Re: gnuplot zoom not functioning anymore in octave 2.9.10

[Daniel J S. <dan...@ie...>]

Ethan A Merritt wrote:

> I think you are missing the worrisome point.  The routine cp_free() works
> its way through a linked list of plots, freeing all dynamically allocated
> space as it goes.  The comment warns that this may fail if there was a call
> to int_error() while one of those dynamically allocated plot structures 
> was in the process of being filled in.  That would hypothetically leave
> invalid links in the linked list, or struct entries that are supposedly
> pointers but contain random garbage.   This really shouldn't happen if 
> everything is initialized in the correct order, but the comment suggests
> that may not be the case. 

Oh, that explains what "first_plot" means.  Also, the "first_plot" is a global. 
  Inside set.c is some strange code.  It doesn't appear to be a bug but I don't 
understand why the f_p and f_3dp had to be used.  Is there a chance cp_free() 
and sp_free() might fail?  If so, the routines shouldn't do that:

     else {
	struct curve_points *f_p = first_plot;
	struct surface_points *f_3dp = first_3dplot;

	first_plot = NULL;
	first_3dplot = NULL;
	cp_free(f_p);
	sp_free(f_3dp);

	iso_samples_1 = tsamp1;
	iso_samples_2 = tsamp2;
     }

Anyway, what I sent last time still applies but at a narrower scope.  For example:

                 if (*tp_ptr)
                     this_plot = *tp_ptr;
                 else {          /* no memory malloc()'d there yet */
                     this_plot = cp_alloc(MIN_CRV_POINTS);
                     *tp_ptr = this_plot;
                 }

"this_plot" shouldn't be moved into the list until after a success.  I.e., move 
the line *tp_ptr = this_plot to the end of the routine.  E.g. (?)

		if (this_plot)
		  cp_free(this_plot);

                 if (*tp_ptr)
                     this_plot = *tp_ptr;
                     *tp_ptr = NULL;
                 else {          /* no memory malloc()'d there yet */
                     this_plot = cp_alloc(MIN_CRV_POINTS);
                 }

		[snip]

                 *tp_ptr = this_plot;


This is a bit messy.  (Little linked-list maintenance routines are always good.) 
  But see what you can do.

Dan