Boost logo

Boost :

From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2007-12-29 10:38:38

Dear Experts,

I have some code which currently uses a std::vector of pointers, and
I'm investigating whether I can make it more concise, exception-safe,
or otherwise better using a ptr_vector. But I can't see a good way to
replace the following code, which shifts part of the vector by one
place, deleting one pointee and creating a new one at the other end:

struct LargeThing { .... };
std::vector<LargeThing*> v;

void shift(int start, int end) {
   delete v[start];
   for (int i=start; i<end; ++i) { // or use a std::algorithm
   v[end] = new LargeThing;

With a ptr_vector, I think that I could do something like

struct LargeThing { .... };
boost::ptr_vector<LargeThing> v;

void shift(int start, int end) {
   v.release(v.begin()+start); // or should that be erase() ?
   v.insert(v.begin()+end-1, new LargeThing);

But this has complexity O(v.length()), because v.release() has to move
all elements beyond start, while my current code has complexity
O(end-start), because it doesn't touch the elements beyond end.

Is there some better way to accomplish this? Maybe transfer() can be
used? Or something involving swap()?

Thanks for any suggestions.


Boost list run by bdawes at, gregod at, cpdaniel at, john at