[Gambas-user] Tests against pointers in Gambas3

[Demosthenes Koptsis]

hello again list,

i am finishing the chapter of pointers soon.

Something last about them.

In C++ books it is suggested after the usage of a pointer to free it and
then assign value 0.

Do you think this advice could be done to Gambas3 like this for safe
programming?

Close #hMemory
Free(pPointer)
pPointer = 0


-----Example ---------------------------------

' Gambas module file

Public Sub Main()

Dim pPointer As Pointer
Dim hMemory As Stream

pPointer = Alloc(4)

Print pPointer

hMemory = Memory pPointer For Read Write
  
Write #hMemory, CByte(0) As Byte
Write #hMemory, CByte(1) As Byte
Write #hMemory, CByte(0) As Byte
Write #hMemory, CByte(1) As Byte

Close #hMemory
Free(pPointer)
pPointer = 0

Print pPointer
Print Byte@(pPointer)

End
-----Example ---------------------------------

Notice with this implementation the last line
Print Byte@(pPointer)
raises an expected error.
Otherwise we still could use the address of pPointer.


On Wed, 2011-01-12 at 17:31 +0100, tobias wrote:
> hi,
> 
> > Hi,
> > 
> > i study the cases of pointers and i found at this page
> > http://www.yolinux.com/TUTORIALS/C++MemoryCorruptionAndMemoryLeaks.html
> > 
> > cases of program crashes from bad usage of pointers.
> > 
> > i made a test for
> > Attempting to write to memory already freed.
> > 
> > ...
> > 
> > in this example i free the pointer and then try to write to it.
> > The result is that i can write and read normally after Free(pPointer)
> > 
> > Is this ok?
> > 
> 
> i noticed the same thing some time ago with a c program. this hasn't to 
> be a bug in gambas... i think this is just as jussi said:
>  > Seems that Gambas still owns that address, but it is not "protected" 
> anymore
> 
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-- 
Regards,
Demosthenes Koptsis.