Cristian Georgescu wrote:
>
> Q: stc container autoresize increment?
> --------------------------------------
>
> Is there possible to specify the number of elements that are
> preallocated when a vector (f.i.) is accessed?
>
> Something like:
>
> vector<int> v;
> v[ 0] =  0; // allocate 10 elements
> //...
> v[10] = 10; // allocate 10 more elements
> //...
>
> This can be achieved manually with reserve() but I would like that this
> is done automatically...

Your code is illegal - even if you use reserve. Just that it happens
to work on your compiler.

vector<int> v;

allocates an empty vector, that is, a vector that contains no elements.

v.reserve(10);

reserves memory for (at least) 10 elements, but it still does contain
*no* *single* *element*!

Note that your code could visibly break if you used a class instead of
int, like the following:

class X // not very useful, but similar things happen in real classes
{
  int* val;
public:
  X(): val(new int) {}
  X(int i): val(new int(i)) {}
  X(const X& x): val(new int(x.val)) {}
  ~X() { delete val; }
  X& operator=(const X& ) { delete val; val=new int(x.val); return
*this; }
};

vector<X> v;
v.reserve(10);
v[0]=X(0);  // and here a segmentation fault (or GPF) is very
probable...


If you want such a "self-expanding vector", you'll have to write it
yourself (probably using vector for implementation).

Alternatively, you could access the vector with a global function
like this:

template<class T> T& access(vector<T> v, int index)
{
  while (v.size() < index)
    v.insert(v.end(),10,T());
  return v[indev];
}


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Q: stc container autoresize increment?
--------------------------------------

Is there possible to specify the number of elements that are
preallocated when a vector (f.i.) is accessed?

Something like:

vector<int> v;
v[ 0] =  0; // allocate 10 elements
//...
v[10] = 10; // allocate 10 more elements
//...

This can be achieved manually with reserve() but I would like that this
is done automatically...

--
                      Cristian Georgescu
_________________________________________________
                      email: CGeorges@lehman.com
                      tel:   (212) 526-3502

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