[fpc-pascal] dynamic array contents and system.move

[David Emerson]

I *am* checking sizes before the move, which is why it surprised me that things 
were going out of bounds -- the trouble is I forgot the array index [0]

On Sat 24 Apr 2010, Martin wrote:
> On 24/04/2010 22:01, Andrew Brunner wrote:
> > David,
> >
> > I don't see how you are not getting memory leaks by doing a move
> > before making sure that the destination buffer has the memory
> > allocated.  You see, in Delphi and FPC, move d/n actually move the
> > memory... It just copies it.
> >
> > You were warned :-)
> >
> > On Sat, Apr 24, 2010 at 3:01 PM, David Emerson<dle3ab at angelbase.com>  wrote:
> >    
> >> cobines wrote:
> >>      
> >>> David Emerson wrote:
> >>>        
> >>>> move (src.f_data, self.f_data, length(self.f_data) * sizeof(byte));
> >>>>          
> >>> I think it should be:
> >>>
> >>> SetLength(self.f_data, length(src.f_data));
> >>> move (src.f_data[0], self.f_data[0], length(self.f_data) * sizeof(byte));
> >>>        
> >>      
> No he doesn't get leaks. If at all he would get crashes, by overwriting 
> random memory.
> 
> But in this case, it's (almost !) save.
> He uses " length(self.f_data)* sizeof(byte)" => so he never copies, more 
> bytes to the target than the target can hold.
> 
> He may however copy bytes from behind the source, reading random memory 
> behind the source. He does not modify this random memory, so far so good 
> => as long as the random meory behind the source is accesible to his 
> process. If it's not accessible, then access violation.
> 
> Martin
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