Re: [RFA] print arrays with indexes

[Joel Brobecker <brobecker@adacore.com>]

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BTW, I forgot to mention a couple of things regarding:

> 2. More annoying, I just tried something else, which is to print an
>    empty Ada array. Ada allows you to create this by using declarations
>    such as this:
> 
>         Table : array (1 .. 0) of Integer;
> 
>    Basically, if the lower/left bound is greater than the right/higher
>    bound, then the array is empty.
> 
>    I just discovered that ada_val_print_1 calls val_print_array_elements
>    even if the array is empty.  This triggers one of the guards in
>    get_array_low_bound(), since the function expects a non-empty array.
> 
>    I'm happy to just put a check in the Ada part to avoid calling
>    val_print_array_elements for empty arrays. This should be fine, but
>    I'm wondering if other languages might be doing the same, in which
>    case it's probably going to be safer to modify a bit
>    val_print_array_elements to handle empty arrays...

  a. I tried with a C example, something like this:

        int table [] = {};

     And verified that GDB worked correctly (printed the address
     of the array, but no value). So there is no issue with C,
     at least. Don't have a pascal compiler handy, though.

  b. I prefer the second approach. It just feels safer and more elegant.
     In fact I just finished testing the attached patch. I will submit
     a proper patch together with a testcase tomorrow.

-- 
Joel

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Index: valprint.c
===================================================================
RCS file: /cvs/src/src/gdb/valprint.c,v
retrieving revision 1.55
diff -u -p -r1.55 valprint.c
--- valprint.c	3 Oct 2005 21:21:20 -0000	1.55
+++ valprint.c	4 Oct 2005 07:40:59 -0000
@@ -959,19 +959,21 @@ val_print_array_elements (struct type *t
   unsigned int rep1;
   /* Number of repetitions we have detected so far.  */
   unsigned int reps;
-  long low_bound_index;
-
-  if (!get_array_low_bound (type, &low_bound_index))
-    {
-      warning ("unable to get low bound of array, using zero as default");
-      low_bound_index = 0;
-    }
+  long low_bound_index = 0;
 
   elttype = TYPE_TARGET_TYPE (type);
   eltlen = TYPE_LENGTH (check_typedef (elttype));
   len = TYPE_LENGTH (type) / eltlen;
   index_type = TYPE_INDEX_TYPE (type);
 
+  /* Get the array low bound.  This only makes sense if the array
+     has one or more element in it.  */
+  if (len > 0 && !get_array_low_bound (type, &low_bound_index))
+    {
+      warning ("unable to get low bound of array, using zero as default");
+      low_bound_index = 0;
+    }
+
   annotate_array_section_begin (i, elttype);
 
   for (; i < len && things_printed < print_max; i++)