Re: Ada Pointer Problem

[aschwarz1309@att.net]

Thanks.

However, if the object is declared in a scoped environment it would seem that the only way that a pointer error could occur would be with explicit exporting of a value. Wouldn't checking this be a more reasonable approach than rejecting benign instances (for the next iteration of Ada)?

EXAMPLE: (or am I missing the point?)

    with Pkg;

    package body David is
      Object_Ptr : Pkg.Ptr_Type;

       procedure P1( Ptr  : out Pkg.Ptr_Type ) is
         P1_Object_Ptr : Pkg.Ptr_Type;

         procedure P1_P1( Ptr : out Pkg.Ptr_Type ) is
            P1_P1_Object_Ptr : Pkg.Ptr_Type;
         begin -- P1_P1
            P1_P1_Object_Ptr  := <local something>'Access;  -- no harm so far
            P1_Object_Ptr     := P1_P1_Object_Ptr;          -- error
            Object_Ptr        := P1_P1_Object_Ptr;          -- error
            Ptr               := P1_P1_Object_Ptr;          -- error
         end P1_P1;

         begin -- P1
            P1_Object_Ptr  := <local something>'Access;  -- no harm so far
            Object_Ptr     := P1_P1_Object_ptr;          -- error
            Ptr            := P1_Object_Ptr;             -- error
         end P1;
    end David;



> The problem is that Object is local to procedure B, while
> X_Ptr is declared at library level (i.e., non-local).
> 
> The principle is that Object exists only when procedure B is
> executing, and what is trying to be prevented is having a value
> of type X_Ptr available when Object no longer exists.  This could
> happen if B were not the main procedure, but were instead a
> library-level procedure that could be called by some other
> subprogram.
> 
> Since procedure B is known to the programmer to be the main
> procedure, in this case, if one is using GNAT, one could
> use the 'Unrestricted_Access attribute, instead of the 'Access
> attribute, and do what you want.
> 
> ----- Original Message ----- 
> From: "skidmarks" <aschwarz@acm.org>
> Newsgroups: comp.lang.ada
> To: <comp.lang.ada@ada-france.org>
> Sent: Friday, October 01, 2004 10:26 AM
> Subject: Ada Pointer Problem
> 
> 
> > Each Ptr assignment below yields the following error message:
> >
> > --    9.    Ptr     : a.X_Ptr  := Object'Access;
> > --       non-local pointer cannot point to local object
> >
> > In the past, the only way that I seem to be able to fix the problem is to
> > put the pointer and assignment in global space (either in file global or
> > in a package spec). I've looked at Ada as a Second Language (Cohen) and,
> > with less diligence, at the Ada LRM but can't figure what I'm doing wrong.
> > What am I doing wrong?
> >
> > thanks
> > art
> >
> > -----------------------------------------------------------
> > -----------------------------------------------------------
> >
> > package a is
> >    type X     is new Integer;
> >    type X_Ptr is access all X;
> > end a;
> >
> > --------------------------------------------------------
> >
> > -- Main Program
> >
> > with a;
> >
> > Procedure b is
> >    subtype Y         is a.X;
> >    subtype Y_Ptr     is a.X_Ptr;
> >
> >    Object  : aliased a.X;
> >    Object_Y: aliased Y;
> >    Ptr     : a.X_Ptr  := Object'Access;
> >    Ptr_Y   : Y_Ptr    := Object'Access;
> >    Ptr_OY  : a.X_Ptr  := Object'Access;
> >    Ptr_1Y  : Y_Ptr    := Object'Access;
> >
> > begin -- b
> >    Ptr     := Object'Access;
> >    Ptr_Y   := Object'Access;
> > end b;
> > _______________________________________________
> > comp.lang.ada mailing list
> > comp.lang.ada@ada-france.org
> > http://www.ada-france.org/mailman/listinfo/comp.lang.ada
> >
>