[fpc-pascal]absolute identifier

Full_Name memsom at post.interalpha.co.uk
Wed Apr 10 17:31:48 CEST 2002

Quoting Jonas Maebe <jonas at zeus.rug.ac.be>:

> On dinsdag, maart 26, 2002, at 04:43 , ron wilson wrote:
> > so in my application, yyleng is referencing the length of the string,
> > yytext, by using the absolute identifier.  i thought i could change
> all
> > references to yyleng to length(yytext), but the lexer often assigns 
> > yyleng
> > manually (ugh!), e.g. yyleng:=n; OR inc(yyleng);.
> You can use setlength(yytext,n) and setlength(yytext,length(yytext)+1) 
> in those cases. But when you're using ansistrings, make sure you do 
> those length adaptions *before* you write anything past the previous 
> end-of-string, since otherwise you'll get segmentation faults.

This is why I suggested using a class earlier. If he used a property he could 
have an internal variable that did the job.

Actually, inc-ing an absolute is stupid in this respect, because pascal will 
not allow you to read past the end of the string anyway (not in Delphi 5)

try the following:

  s: string[10];
  sa: Byte absolute s;
  a: Integer;

procedure Test
  s := '1234567890';
  a := sa;
  s[a] := 'a';
  ShowMessage(IntToStr(Length(s)) + ' ' + s + ' ' + s[a]);

  a := sa;
  s[a] := 'b';
  ShowMessage(IntToStr(Length(s)) + ' ' + s + ' ' + s[a]);

The above works up to a point, but is really unstable. The second showmessage 
is unable to resolve s[a] to be a value.


"Computer games don't affect kids; I mean if Pac-Man affected us as kids, 
we'd all be running around in darkened rooms, munching magic pills and 
listening to repetitive electronic music." 
Kristian Wilson, 
Nintendo, Inc, 1989

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