[fpc-devel] Variants and strings

[Joost van der Sluis]

Hi all,

I've found a problem in the string-implementation of the variants, but I
thought I would better discus it first, before I start doing all sort of
work for nothing.

In variants string-values are stored as PWideChar's. (called vOleStr)
But if you set a string-value to a variant, it's stored and initialized
as a WideString. Widestrings are ref-counted, and since it's getting
casted into a PWideChar, things are going wrong. Example:

var v : variant;
    s : string;

begin
  v := 'Hello World';
  s := v;
  writeln(s);
  s := v;
  writeln(s);
end;

returns only one 'ello World' or in some cases '   d'. That's because in
the assignment (s:=v) the memory of the Widestring is already freed
before it's value is assigned to the string. (A new pwidechar is
initialised at the same memory-location, wich sets the first character
to #0, the termination of the newly-initialised pwidechar)

I've fixed this in changing the assignment-part to use a PWideChar
instead of the Widestring. The problem of that solution is that you have
to allocate memory for the PWideChar. If you change the value of the
variant, memory should be re-allocated. And I'm curious if the memory
will be freed when the variant is freed. Writing all those things would
mean that you're writing all sorts of code, which is already there for
Widestrings!

So I want to suggest to change the string-support in variants form
PWideChar into Widestrings. This is also more Delphi-compatible.
According to the Delphi help strings in variants are stored in
Widestrings...

But as said, before I start changing this I would like to know what your
opinion is on this...

-- 
Met vriendelijke groeten,

  Joost van der Sluis
  CNOC Informatiesystemen en Netwerken
  http://www.cnoc.nl