[fpc-pascal] more questions on storage

[Mattias Gaertner]

On Wed, 26 Sep 2007 16:29:20 +0200 (CEST)
marcov at stack.nl (Marco van de Voort) wrote:

> > Am Mittwoch, den 26.09.2007, 13:24 +0200 schrieb Marco van de Voort:
> > > > > 
> > > > > Ansistrings (and thus {$longstrings on}) work fine.
> > > > 
> > > > Ah, okay. The Fog is lifting fastly. :)
> > > > 
> > > > And AnsiStrings are pretty much compatible to C's char*. Very
> > > > handy.
> > > 
> > > Yes, though ansistrings may contain #0's.
> > 
> > Interesting, how will a cast handle this case?
>  
> > Will it change the intermediate #0 to something else or will the
> > resulting pchars be cut at first occurrence?
> 
> 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));


> It's mostly important when ansisstring is abused as general purpose
> buffer, but generally it is better to use dyn arrays for that.


Mattias