[fpc-pascal] more questions on storage

Marc Weustink marc at dommelstein.net
Thu Sep 27 20:36:24 CEST 2007

Mattias Gaertner wrote:
> On Thu, 27 Sep 2007 12:38:13 +0200 (CEST)
> marcov at stack.nl (Marco van de Voort) wrote:
>>> marcov at stack.nl (Marco van de Voort) wrote:
>>>> A cast is really a cast. IOW the cast pchar(ansistring) is mostly
>>>> a no-op. Traditional C code then usually treats the #0 as end of
>>>> string. 
>>> PChar(AnsiString) was a no-op typecast in the past and is nowadays a
>>> function. It checks whether the AnsiString is nil and if yes
>>> returns a pointer to a string containing one character: #0.
>>> That means:
>>> Pointer(AnsiString) <> Pointer(PChar(AnsiString))
>>> To get a no-op typecase you can use:
>>> MyPChar:=PChar(Pointer(AnsiString));
>> Is this delphi compat, and if yes, what is this exactly for?
> I don't know.
> The change broke some lazarus code and now it is polluted by the ugly
> double type casts, just to get some no-op type casts.
> Because this fact is not widely known or often forgotten, many use the
> PChar() as simple type cast. That's why the lcl interfaces already got
> into troubles several times, so everytime we get strange errors I first
> search for these typecasts.
> Maybe we should mention this fact at a more prominent place in the
> wiki and docs.

Maybe also add another "type" to get the OldTypecase behaviour.

I allways thought that casting through Pointer() did return the real 
allocated data (thus including reference and length)


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