On 2007-09-15 15:09, terminator wrote:
> On Sep 11, 11:03 pm, werasm <wer...@gmail.com> wrote:
>> terminator wrote:
>> > I said huge because a container contains data spatered all over the
>> > heap and when it comes to copy(instead of reference) ,then it does not
>> > matter if the data is stored in a contigeous portion of memory or
>> > segmented into peices on different corners of memory.the actual size
>> > of a container is often much larger than its own data structure(one or
>> > two pointers and intrinsic values as well as the vtable in runtime
>> > polymorphic ones).
>>
>> In that case I don't see how it contributes to your argument of using
>> a pointer to the container instead of the actual container, if I
>> understand you correctly, as whether one uses a pointer to
>> a container, or the container itself, you always going to use the
>> heap, and in the case of a pointer to the container, slightly more
>> than in the other case, as now the pointer members are also on
>> the heap.
>>
>
> only dynamic objects are placed on heap not pointers to objects,also
> pointers can simply point to some stack variable in the presenet
> thread as well.
> The contribution? Very obvious!!! Copying containers is generally both
> memory and runtime consuming and should be avoided whenever
> possible ,and the simplest way is to use ref/ptr semantics.
>
>> As far as inside a container is concerned, it depends on the type
>> T. Typically, if I want to prevent copying, I use either pointers,
>> or even a pointer_container aka. boost::ptr_vector. If copying of
>> the container does not happen often, and T has the relevant
>> members required, then I use T (by value).
>>
>
> I am talking about the container itself, not the elements.If one
> address/refrences a container no element copy is performed but copying
> a container is a nightmare sometimes,eventhough elements are pointers.

Yes, what you say is true, but it is a question of semantics. For some
types the container should be copied for some it should not, you should
only use pointers where the containers are shared (and perhaps not even
then, you can use "smart" containers instead).

--
Erik Wikström