[Gambas-user] Tests against pointers in Gambas3

[Jussi Lahtinen]

Seems that Gambas still owns that address, but it is not "protected" anymore
and so it can be used to other purposes.
I'm not sure when Gambas *actually* frees that address.

There are fundamental problems when you compare C/C++ and any basic language
in this way.
Same line in C may mean very different thing than in basic.
Basic languages are high level languages (
http://en.wikipedia.org/wiki/High-level_programming_language ),
they hide much from you about what actually happens.
Even one simple line of code in basic can mean many many lines in machine
code.
That makes them user friendly (you don't have to know all details and write
so much code), but also slower.

Hello world, in assembly (low level language);

section	.text
    global _start			;must be declared for linker (ld)

_start:					;tell linker entry point

	mov	edx,len	;message length

	mov	ecx,msg	;message to write
	mov	ebx,1	;file descriptor (stdout)
	mov	eax,4	;system call number (sys_write)
	int	0x80	;call kernel

	mov	eax,1	;system call number (sys_exit)
	int	0x80	;call kernel

section	.data

msg	db	'Hello, world!',0xa	;our dear string
len	equ	$ - msg			;length of our dear string



in C (not *that* low level);

#include<stdio.h>

main()

{
    printf("Hello world");
}


in Gambas (high level language);

Public Sub Main()
Print "Hello world"
End


Gambas uses technology called bytecode interpreter.
http://en.wikipedia.org/wiki/Interpreter_%28computing%29

Jussi




On Tue, Jan 11, 2011 at 19:32, Demosthenes Koptsis
<demosthenesk at ...626...>wrote:

> 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.
>
> ---------------------------
> ' Gambas module file
>
> Public Sub Main()
>
> Dim pPointer As Pointer
> Dim hMemory As Stream
>
> pPointer = Alloc(SizeOf(gb.Integer))
> hMemory = Memory pPointer For Read Write
>
> Print pPointer
>
> Free(pPointer)
>
> Write #hMemory, 10 As Integer
>
> Print pPointer
> Print Int@(pPointer)
> Print pPointer
>
> End
> ---------------------------
>
> 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?
>
> --
> Regards,
> Demosthenes Koptsis.
>
>
>
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