How to define vectors in an existing vector ?

[lalebarde]

Hi all,
I have defined a big vector :

vector<int> v(1000000);

If I initialise it like this :

for (int i = 0; i < 1000000; i++) v[i] = i;

I would like to do something like the following pseudo-code :

vector<int>* pv1 = &(v[1618]), pv2 = &(v[1620]);
pv1->size = 4;
pv2->size = 3;

To obtain :

ostream_iterator<int> out(cout, " ");
cout << "pv1 = "; copy(pv1->begin(), pv1->end(), out); cout << endl;
cout << "pv1 = "; copy(pv1->begin(), pv1->end(), out); cout << endl;

pv1 = 1618 1619 1620 1621
pv2 = 1620 1621 1622

How to do that with vectors ?
I can do it with arrays, but I would like to stay with vectors if possible.

[fanasy]

template <class InputIterator> vector ( InputIterator first, InputIterator last, const Allocator& = Allocator() );

Iteration constructor: Iterates between first and last, setting a copy of each of the sequence of elements as the content of the container.

is constructor may meet your request.

[lalebarde]

Thanks for your answer fanasy, but this constructor makes copies, what is not acceptable for me because I have to manipulate huge chunks of data.

[guestgulkan]

If the object of the exercise is just to ouput some sub_part of the original vector - then
there is no need to make new vectors - just set a vector_iterator ( lets call it pv1) to the first element, loop until pv1+x (where x is the number of elements required to output).

However, if you really want to create a second vector then you have no choice but to copy.
(I'm waiting...)

NOTE: certainly in the context of an ostream iterator, the copy function does not actually make
a copy (it doesn't need to) - it just does the usual ostream << object
thing.

[lalebarde]

Thanks guestgulkan. Of course, my example is simple for clarity.

So I am back to arrays.

Thought, to clarify my need : I want to create a big hash table class that will be loaded in shared memory with a lot of methods using side tables of different sizes. So I want these tables to be stored in a continuous array of memory.