Re: Access of elements of a string constant

[Michael Riedl]

Hallo John,

had a look in the standard (only have a late draft at hand).

Would not have interpreted that in the sense you indicated, but it seems 
you are right !

So I recoded to ...

MODULE TstStrConst;

IMPORT STextIO,SWholeIO;

CONST len     = 16;

TYPE  TNumStr = ARRAY [0..len-1] OF CHAR;

CONST NumStr  = TNumStr{ (* "0123456789ABCDEF" *)
                 "0","1","2","3","4","5","6","7","8","9",
                 "A","B","C","D","E","F"
               };

VAR   i : CARDINAL;
      c : CHAR;
BEGIN
      STextIO.WriteLn;
      FOR i:=0 TO len-1 DO
        SWholeIO.WriteCard(i,2);
        STextIO.WriteString(" '");
        c := NumStr[i];
        STextIO.WriteChar(c);
        STextIO.WriteString("' ");
        SWholeIO.WriteCard(ORD(c),1);
        STextIO.WriteLn;
      END;
      STextIO.WriteLn;
END TstStrConst.

This is compiled but does not give the expected result on my machine ...

Should be

 0 '0' 48
 1 '1' 49
 2 '2' 50
 3 '3' 51
 4 '4' 52
 5 '5' 53
 6 '6' 54
 7 '7' 55
 8 '8' 56
 9 '9' 57
10 'A' 65
11 'B' 66
12 'C' 67
13 'D' 68
14 'E' 69
15 'F' 70

but ends up with

 0 '0' 48
 1 '' 0
 2 '' 0
 3 '' 0
 4 '' 0
 5 '' 0
 6 '' 0
 7 '' 0
 8 '' 0
 9 '' 0
10 '' 0
11 '' 0
12 '' 0
13 '' 0
14 '' 0
15 '' 0

interrestingly the fist line is OK ...

Any idea ?

If I use a construct like

...

CONST digits = "0123456789ABCDEF"

VAR   Digits = ARRAY [0..15] OF CHAR; (* do not need the terminating "0C" *)

BEGIN

      Digits := digits;

...

all seems fine ..

Michael


PS: By the way, does anybody in the audience know if my original code 
would be OK in PIM ? Just for interest.


Am 05.01.20 um 03:00 schrieb john o goyo:
> Greetings, Michael.
>
> On 01/04/20 12:05, Michael Riedl wrote (in part):
> > [...]
> >
> > MODULE TstStrConst;
> >
> > IMPORT STextIO,SWholeIO;
> >
> > CONST NumStr = "0123456789ABCDF";
> >
> > VAR   i : CARDINAL;
> >
> > BEGIN
> >       STextIO.WriteLn;
> >       FOR i:=0 TO LENGTH(NumStr)-1 DO
> >         SWholeIO.WriteCard(i,2);
> >         STextIO.WriteString(" '");
> >         STextIO.WriteChar(NumStr[i]);
> >         STextIO.WriteString("' ");
> >         SWholeIO.WriteCard(ORD(NumStr[i]),1);
> >         STextIO.WriteLn;
> >       END;
> >       STextIO.WriteLn;
> > END TstStrConst.
> >
> > It can be fixed by a VAR string initialized in the module body - but 
> > that's less elegant.
> I know not about PIM but that construct seems to be disallowed by ISO:
>
>     NOTE 1 - An indexed value cannot be formed by indexing a string 
> constant.
>
>     (ISO/IEC 10514-1, Sect. 6.8.4.2)
>
> john