Modifying string length?_(re)

Fri, 2 May 1997 03:26:20 +0200 (MET DST)

According to Frank Heckenbach:
> 
> s:='' should do the same. (BP optmizes this to just setting the length to 0,
> I hope gpc does as well.)

It does.  (But better check it, too - I already was wrong once with
statements of this type.;-)

> I think it should (at least with {$X+} or such), because it's the only way
> to translate some kinds of procedures -- unless one wants to limit such
> procedures to borland-like short strings.

Long strings:  "S.length:= ...".  Short strings: "S [ 0 ]:= chr ( ... )".

> The question is, should the #0 be added for short strings as well?
> If Length=Capacity, it's impossible, but otherwise???

We could increase the space allocated for a short string by 1, but this
would break compatibility to UCSD and Borland Pascal.  So better ignore
this and live with "String [ 255 ]" having only a capacity of 254 in fact.

> Currently the length could probably be changed by writing to
> s[1-SizeOf(Integer)] .. s[0] -- but I really don't want to try that... :-|

No.  This will only work for lenghts below 256 and on big-endian machines.
Better cast the String to a record (read: cast a pointer to the String to
a pointer to a record).

> BTW: Does the standard require range checking (or does it say anything about
> it at all)?

Yes, AFAIK.

> And with {$X-} they don't work at all, you mean? Seems ok.
> And the same for packed records?

Yes.

> Isn't it good when non-standard compilers (BP) use non-standard syntax? :-)

I would not call this "non-standard" since this - like many other things,
e.g. Units - was not invented by Borland but by UCSD.

> BTW: String[n] with n>255 wouldn't work at all then?

Yes.

Greetings,

    Peter

  Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer
peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201]
 maintainer GNU Pascal [970420] - http://home.pages.de/~gnu-pascal/ [970125]

Peter Gerwinski (peter@agnes.dida.physik.uni-essen.de)