problemn with string'last

problemn with string'last

[Daniel Gaudry]

hi,
here is a code that i simplified

with Ada.Text_Io;
procedure Help
   is
   Double_Quote : constant String(1 .. 1) := (others => '"' );
   Data         : constant String         := "  PLUS_STRING    : CONSTANT STRING(1..3) :=(1 =>'" & Double_Quote & "' , 2 =>'+' , 3 =>'" & Double_Quote & ");";
   begin
 
   Ada.Text_Io.Put_Line("     05   10   15   20   25   30   35   40   45   50   55   65   70   75   80   85   90");
   Ada.Text_Io.Put_Line(" ....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!");
   Ada.Text_Io.Put_Line("»" & Data & "« " & Data'Last'Img);
 
end Help;


but the data'last seems not to match the string size

Any help is welcome
best regards

Re: problemn with string'last

[Dmitry A. Kazakov]

On 2023-05-05 11:51, Daniel Gaudry wrote:

> here is a code that i simplified
> 
> with Ada.Text_Io;
> procedure Help
>     is
>     Double_Quote : constant String(1 .. 1) := (others => '"' );
>     Data         : constant String         := "  PLUS_STRING    : CONSTANT STRING(1..3) :=(1 =>'" & Double_Quote & "' , 2 =>'+' , 3 =>'" & Double_Quote & ");";
>     begin
>   
>     Ada.Text_Io.Put_Line("     05   10   15   20   25   30   35   40   45   50   55   65   70   75   80   85   90");
>     Ada.Text_Io.Put_Line(" ....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!");
>     Ada.Text_Io.Put_Line("»" & Data & "« " & Data'Last'Img);
>   
> end Help;
> 
> but the data'last seems not to match the string size

It matches. You missed the "60" tick in your scale. (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: problemn with string'last

[Jeffrey R.Carter]

On 2023-05-05 11:51, Daniel Gaudry wrote:
>   
>     Ada.Text_Io.Put_Line("     05   10   15   20   25   30   35   40   45   50   55   65   70   75   80   85   90");
>     Ada.Text_Io.Put_Line(" ....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!....|....!");
>     Ada.Text_Io.Put_Line("»" & Data & "« " & Data'Last'Img);

As Kazakov pointed out, your scale is incorrect.

However, it's important to remember that 'Last is not necessarily the same as 
'Length because 'First is not necessarily one. This is especially important in 
subprograms that take String parameters, as they are often passed slices.

Some questions:

>    Double_Quote : constant String(1 .. 1) := (others => '"' );

ARM 2.1(15/3) 
(http://www.ada-auth.org/standards/aarm12_w_tc1/html/AA-2-1.html#I1199) defines 
the name of '"' as "quotation mark". Why do you refer to a single quotation mark 
as Double_Quote?

>    Data         : constant String         := "  PLUS_STRING    : CONSTANT STRING(1..3) :=(1 =>'" & Double_Quote & "' , 2 =>'+' , 3 =>'" & Double_Quote & ");";

Wouldn't it be simpler and clearer to write this as

Data : constant String := "  PLUS_STRING : CONSTANT STRING := " & '"' & '+' & '"';

? Note also that you seem to be missing an apostrophe (''') before the right 
parenthesis if you intend Data to be a valid Ada declaration.

-- 
Jeff Carter
"All citizens will be required to change their underwear
every half hour. Underwear will be worn on the outside,
so we can check."
Bananas
29

Re: problemn with string'last

[Dmitry A. Kazakov]

On 2023-05-05 13:17, Jeffrey R.Carter wrote:

> However, it's important to remember that 'Last is not necessarily the 
> same as 'Length because 'First is not necessarily one. This is 
> especially important in subprograms that take String parameters, as they 
> are often passed slices.

Non-sliding indices is one of the most useful Ada features. You can pass 
indices around as-is, which is extremely helpful when processing strings.

You will also find that actually 'Length and 'Last have different types, 
which is quite useful as well.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: problemn with string'last

[Manuel Gomez]

El 5/5/23 a las 13:17, Jeffrey R.Carter escribió:
> On 2023-05-05 11:51, Daniel Gaudry wrote:
>>    Data         : constant String         := "  PLUS_STRING    : 
>> CONSTANT STRING(1..3) :=(1 =>'" & Double_Quote & "' , 2 =>'+' , 3 =>'" 
>> & Double_Quote & ");";
> 
> Wouldn't it be simpler and clearer to write this as
> 
> Data : constant String := "  PLUS_STRING : CONSTANT STRING := " & '"' & 
> '+' & '"';
> 
> ? Note also that you seem to be missing an apostrophe (''') before the 
> right parenthesis if you intend Data to be a valid Ada declaration.
> 

Or like this (doubling the quotes, which is the way to _escape_ the 
double quote inside Ada strings):

    Data         : constant String         := "  PLUS_STRING    : 
CONSTANT STRING(1..3) :=(1 =>'""' , 2 =>'+' , 3 =>'""');";

Re: problemn with string'last

[Simon Wright]

Manuel Gomez <mgrojo@gmail.com> writes:

> Or like this (doubling the quotes, which is the way to _escape_ the
> double quote inside Ada strings):
>
>    Data         : constant String         := "  PLUS_STRING    :
>    CONSTANT STRING(1..3) :=(1 =>'""' , 2 =>'+' , 3 =>'""');";

'"' is a single quote character.
"""" is a string containing one quote character.

Re: problemn with string'last

[Manuel Gomez]

El 5/5/23 a las 18:33, Simon Wright escribió:
> Manuel Gomez <mgrojo@gmail.com> writes:
> 
>> Or like this (doubling the quotes, which is the way to _escape_ the
>> double quote inside Ada strings):
>>
>>     Data         : constant String         := "  PLUS_STRING    :
>>     CONSTANT STRING(1..3) :=(1 =>'""' , 2 =>'+' , 3 =>'""');";
> 
> '"' is a single quote character.
> """" is a string containing one quote character.

Yes, and "'""'" is a string containing a quote as an Ada character (when 
displayed).

Re: problemn with string'last

[J-P. Rosen]

Le 05/05/2023 à 20:18, Manuel Gomez a écrit :
> Yes, and "'""'" is a string containing a quote as an Ada character (when 
> displayed).

Even more fun (I use this for people who write a naive Ada parser):
    subtype C is Character;
    V : String := C'(')')'Img;

-- 
J-P. Rosen
Adalog
2 rue du Docteur Lombard, 92441 Issy-les-Moulineaux CEDEX
https://www.adalog.fr https://www.adacontrol.fr

Re: problemn with string'last

[Simon Wright]

Manuel Gomez <mgrojo@gmail.com> writes:

> El 5/5/23 a las 18:33, Simon Wright escribió:
>> Manuel Gomez <mgrojo@gmail.com> writes:
>> 
>>> Or like this (doubling the quotes, which is the way to _escape_ the
>>> double quote inside Ada strings):
>>>
>>>     Data         : constant String         := "  PLUS_STRING    :
>>>     CONSTANT STRING(1..3) :=(1 =>'""' , 2 =>'+' , 3 =>'""');";
>> '"' is a single quote character.
>> """" is a string containing one quote character.
>
> Yes, and "'""'" is a string containing a quote as an Ada character
> (when displayed).

Oh, I see. Ugh.

Re: problemn with string'last

[Jeffrey R.Carter]

On 2023-05-05 22:44, Simon Wright wrote:
> Manuel Gomez <mgrojo@gmail.com> writes:
> 
>> El 5/5/23 a las 18:33, Simon Wright escribió:
>>> Manuel Gomez <mgrojo@gmail.com> writes:
>>>
>>>>      Data         : constant String         := "  PLUS_STRING    :
>>>>      CONSTANT STRING(1..3) :=(1 =>'""' , 2 =>'+' , 3 =>'""');";
>>> '"' is a single quote character.
>>> """" is a string containing one quote character.
>>
>> Yes, and "'""'" is a string containing a quote as an Ada character
>> (when displayed).
> 
> Oh, I see. Ugh.

As you have discovered, using doubled quotation marks within a String literal 
can be significantly less clear than concatenating the quotation-mark Character 
with the rest of the String.

-- 
Jeff Carter
"All citizens will be required to change their underwear
every half hour. Underwear will be worn on the outside,
so we can check."
Bananas
29