Re: Table of pointers question

[Adam Beneschan <adam@irvine.com>]

On Sep 23, 11:59 pm, Georg Bauhaus <rm.tsoh.plus-
bug.bauh...@maps.futureapps.de> wrote:
> Rob Solomon wrote:
> > I am working my way thru Ada As A Second Language by Norman Cohen (c)
> > 1996
>
> > This confuses me.
>
> > It is a simple sorting routine that swaps pointers rather than the
> > data.  Note that the variables are more like Modula-2 syntax as I am
> > very comfortable with that.  And it is easier to type.
>
> Has something gone wrong when (I'm guessing here) the
> program was rewritten for Ada?  The compiler shows some
> errors.  After correcting these formally, i.e. without thinking,
> it confirms Adam's observation, and hints to others:
>
> Compiling: printdirectory.adb (source file time stamp: 2009-09-24 06:42:50)
>
>     25.   EntryList        : array (1..MaxEntries) of DirectoryEntryType;
>           |
>         >>> warning: variable "EntryList" is not referenced
>
>     33.     NewEntry.NamePart := To_Bounded_String(Buffer(1..Length));
>             |
>         >>> warning: "NewEntry" may be null
>
> Here, the "correction" was
> 1 -  END IF;  -- semicolon, not colon
> ...
> 2, 3 -    EntryPointerList(NumberOfEntries) := -- *new*
> DirectoryEntry*Pointer*Type'(NewEntry);  -- MY QUESTION HERE
>
> (NewEntry is of a pointer type already.)

That's the error.  NewEntry should not be a pointer type.  The intent
appears to be that a record of type DirectoryEntryType is built, and
then a copy of it allocated on the heap and the pointer stored in the
array.  (I'm assuming that's the case; I don't have Cohen's book
handy.)

So the declaration of NewEntry is wrong.  Perhaps that has to do with
a misunderstanding of the relationship between pointers and data; but
I think it's more likely just a typographical error, made harder to
spot by the lack of underscores.

                                     -- Adam