Thanks! But is there any more? I'm not a computer scientist, just an electrical
engineer who learnt how to program tutorial-style. I really don't know what
heap or stack memory is. And wikipedia isn't very helpful. Do you know of any
book that explains this matters?
Thanks!
---------------------------------------
Sergio Campamá
sergiocamp...@gmail.com
On Sep 29, 2011, at 6:25 PM, David Brown wrote:
> On 29/09/11 21:00, Sergio Campamá wrote:
>> On Thu, Sep 29, 2011 at 3:55 PM, David
>> Brown<david.br...@hesbynett.no>wrote:
>>
>>> On 29/09/11 20:52, Sergio Campamá wrote:
>>>> Hello,
>>>>
>>>> I was under the impression that in C you could not do something
>>>> like:
>>>>
>>>> void func(int size) { int array[size]; //something return; }
>>>>
>>>> But a friend of mine just proved me wrong, using mspgcc...
>>>> Searching around we found this to be VLA (variable length array)
>>>> Does this kind of usage fall into dynamic memory? My impression
>>>> is that the answer is yes, and therefore it shouldn't be used on
>>>> microprocessors, because malloc can cause havoc (as someone told
>>>> me some emails ago in this very same group).
>>>>
>>>> What are your thoughts on VLA? Does it use malloc internally, and
>>>> therefore should be avoided?
>>>>
>>>
>>> Variable length arrays are like any other data - they can go in
>>> various places. In a case like this, you have defined a non-static
>>> local variable - just like any other non-static local variable, it
>>> goes on the stack. So as long as you are careful not to overflow
>>> your stack, this should be fine - it doesn't suffer from the risks
>>> you get with malloc (or, more accurately, the risks you get with
>>> free), namely unpredictably long delays, fragmented heaps, and no
>>> space errors.
>>>
>> Thanks David. I have been meaning to understand fully well how
>> memory works in terms of stack and ram. Is there any text or
>> resource available that could help me understand that?
>>
>
> It's basic C. Anything defined with a static lifetime (global data,
> static local data) is statically allocated at fixed memory addresses.
> Anything local to a function is either kept in registers (or removed
> altogether by the optimiser) or put on the stack. Anything allocated by
> malloc (or standard "new" in C++) goes on the heap.
>
>
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