[fpc-pascal] Question: range checking for string indexing

[Vinzent Höfler]

Tom Verhoeff wrote:

> I am surprised that for ShortString, the range is not
> also 1 <= i <= Length(s).
> 
> IIRC Turbo Pascal only allowed you to access s[0] when range checking
> was off, and similarly for s[i] with i > Length(s).

No. See transcript:

-- 8< -- the program --
{$R+}

var
    s1 : String;
    s2 : String[40];

begin
   s1 := '';
   s2 := '';

   WriteLn (Length (s1));
   WriteLn (Length (s2));

   WriteLn (Ord (s1[0]));
   WriteLn (Ord (s2[0]));

   WriteLn (Ord (s1[255]));
   WriteLn (Ord (s2[255]));
end.
-- 8< --

results in:

-- 8< --
Borland Pascal  Version 7.0  Copyright (c) 1983,92 Borland International
TEST.PAS(18): Error 76: Constant out of range.
   WriteLn (Ord (s2[255]));
                       ^
-- 8< --

Commenting out the offending last line of code:

-- 8< --
Borland Pascal  Version 7.0  Copyright (c) 1983,92 Borland International
TEST.PAS(19)
19 lines, 2432 bytes code, 968 bytes data.
-- 8< --

Running the program:

-- 8< --
.\TEST.EXE
0
0
0
0
0
-- 8< --

No errors, although the index exceeds the actual length of the string.


Vinzent.