Re: unsigned type

[anon@anon.org (anon)]

--
-- Just a side note.   Found while using a search engine.
--
with Ada.Text_IO ;
use  Ada.Text_IO ;

procedure Temp is

    C : constant String := ( 1..0 => 'A' ) ; 
    --
    --  So, what happens to the 'A' and why does the compiler allow 
    --  the constant 'A' when it result will be a null array.
    --
    --  If you use ( 1..0 => 'A' ) you must provide an unusable single
    --  Character, double quotes or emply quote are illegal.  Logic 
    --  suggest that the statement should be
    --  C : constant String := ( 1..0 => '' ) ;
    --
    D : constant String := "" ; 

begin

  Put_line ( "C => '" & C & "'  =  '" & C ( 1..0 ) & "'" ) ;
  New_Line ;

  Put_Line ( "is C equal to D => " & Boolean'Image ( C = D ) ) ;
  New_Line ;
 
end Temp ;


In <4b83m.98382$d36.15650@bgtnsc04-news.ops.worldnet.att.net>, anon@anon.org (anon) writes:
>--  Adam. 
>--    Now, can you please explain the results from this program.
>--
>--    It just does not make sense.  Because in the second pass though  
>--    Test.Put the bounds for String is ( 1..1 ) but if the procedure 
>--    uses a String ( 2 .. -2 ) which neither index is not within the 
>--    valid subscript range. And this is also echoed in the third pass.
>--
>--    Note: The RM uses ( 1 .. 0 ) but allows ( L .. R ) if L > R, for
>--           null arrays.  But I think the RM and ACATS suggest that the 
>--           Left side index needs to be a valid subscript of the array.
>--           Which make B ( 2 .. -2 ) illegal if the B String is bound
>--           by ( 1 .. 1 ).
>--
>with Ada.Integer_Text_IO ;
>with Ada.Text_IO ;
>with Ada.Exceptions ;
>
>procedure Test is
>
>  use Ada.Exceptions ;
>  use Ada.Integer_Text_IO ;
>  use Ada.Text_IO ;
>
>  C : String := "This is a test string" ;
>
>  --
>  -- Define a Put routine for String type.
>  --
>  procedure Put ( B : String ) is
>
>    begin
>      New_Line ;
>      Ada.Text_IO.Put ( "    B'( " ) ;
>      Put ( B'First ) ;
>      Ada.Text_IO.Put ( " .. " ) ;
>      Put ( B'Last ) ;
>      Ada.Text_IO.Put ( " ) => " ) ;
>      Ada.Text_IO.Put_Line ( ( B ( B'First .. B'Last ) ) ) ;
>
>      Ada.Text_IO.Put ( "    B'( 2 .. -2 ) => '" ) ;
>      Ada.Text_IO.Put ( ( B ( 2 .. -2 ) ) ) ;
>      Ada.Text_IO.Put ( ''' ) ;
>      New_Line ( 2 ) ;
>    end Put ;
>
>begin
>
>  Ada.Text_IO.Put_line ( "Normal String Print  --  Valid" ) ;
>  Ada.Text_IO.Put ( "C ( C'First .. C'Last ) => " ) ;
>  begin
>    Test.Put ( C ( C'First .. C'Last ) ) ;
>  exception
>    when E : Constraint_Error =>
>      Ada.Text_IO.Put_Line ( Exception_Name ( E ) & 
>                             " => " &
>                             Exception_Message ( E ) ) ;
>  end ;
>  New_Line ;
>
>  Ada.Text_IO.Put_line ( "Normal Sub String Print  --  Invalid???" ) ;
>  Ada.Text_IO.Put ( "C ( C'First .. C'First ) => " ) ;
>  begin
>    Test.Put ( C ( C'First .. C'First ) ) ;
>  exception
>    when E : Constraint_Error =>
>      Ada.Text_IO.Put_Line ( Exception_Name ( E ) & 
>                             " => " &
>                             Exception_Message ( E ) ) ;
>  end ;
>  New_Line ;
>
>
>  Ada.Text_IO.Put_line ( "Normal Sub String Print  --  Invalid???" ) ;
>  Ada.Text_IO.Put ( "C ( ( C'First + 4 ) .. ( C'Last - 4 ) ) => " ) ;
>  begin
>    Test.Put ( C ( ( C'First + 4 ) .. ( C'Last - 4 ) ) ) ;
>  exception
>    when E : Constraint_Error =>
>      Ada.Text_IO.Put_Line ( Exception_Name ( E ) & 
>                             " => " &
>                             Exception_Message ( E ) ) ;
>  end ;
>  New_Line ;
>
>end Test ;
>
>In <273dedb7-8d68-42d2-8602-aa44c79f3708@b9g2000yqm.googlegroups.com>, Adam Beneschan <adam@irvine.com> writes:
>>On Jun 30, 4:48=A0pm, a...@anon.org (anon) wrote:
>>> Read RM 3.5 =A0( 4 )
>>>
>>> Is "A ( 0 .. 0 )" an example of null range. =A0By the definition in RM 3.=
>>5
>>> ( 4 ), the Right side range (index) must be less than the Left side, so
>>> "A ( 0.. 0 )" is not a valid null range statement. So, this statement
>>> should generate a compiler or runtime error, because either range is not
>>> a subset of the range for Strings.
>>
>>OK, I think I've finally figured out why we're having this confusing
>>argument.  It goes way back to this post of yours:
>>
>>>> For Strings:
>>>>                          --  'A' is a zero length string, A'Last =3D 0, =
>>and
>>>>                          --  put_line  ( A ( A'First .. A'Last ) ) ;
>>>>                          --  does not raise an Constraint_Error even tho=
>>ugh in
>>>>                          --  this case it translate to:
>>>>                          --  put_line  ( A ( 0 .. 0 ) ) ;
>>>>  A : String :=3D ""        ;
>>
>>It does not translate to A (0..0); it translates to A (1..0).  If A is
>>declared as in your example above, A'First will be 1 and A'Last will
>>be 0.  Try it (try declaring A like that and outputting A'First and
>>A'Last).  It looks like everyone else missed this original error of
>>yours, which has apparently led to some confusion.
>>
>>In this case, A'First..A'Last, which is 1..0, is compatible with the
>>subtype because it's a null range, and null ranges are compatible with
>>the subtype even when the range bounds don't actually belong to the
>>subtype.  0..0 is not compatible with the subtype, but you cannot
>>declare a string with that index range unless you try to do it
>>explicitly:
>>
>>   A : String (0..0);
>>
>>and then you *will* get a Constraint_Error.
>>
>>So your later assertion that follows:
>>
>>>> Since you can have zero length string , the index is Natual instead of P=
>>ositive,
>>>> because zero is in Natural but is not define in Positive. Even though th=
>>e
>>>> Standard package define String index as a Positive type. (GNAT)
>>
>>is wrong.  The index range is Positive, but null ranges don't have to
>>meet that constraint.  They don't have to be Natural, either.  This is
>>legal and will not raise an exception at runtime:
>>
>>   B : String (-9 .. -10) :=3D "";
>>
>>Hope this clears everything up.
>>
>>                                  -- Adam
>>
>