Many C++ programmers have ever wondered where does good old realloc fit in C++. And that's a good question. Could we improve vector performance using memory expansion mechanisms to avoid too many copies? But vector is not the only container that could benefit from an improved allocator interface: we could take advantage of the insertion of multiple elements in list using a burst allocation mechanism that could amortize costs (mutex locks, free memory searches...) that can't be amortized when using single node allocation strategies.

These improvements require extending the STL allocator interface and use make use of a new general purpose allocator since new and delete don't offer expansion and burst capabilities.

Use them simply specifying the new allocator in the corresponding template argument of your favourite container:

#include <boost/container/vector.hpp>
#include <boost/container/flat_set.hpp>
#include <boost/container/list.hpp>
#include <boost/container/set.hpp>

//"allocator" is a general purpose allocator that can reallocate
//memory, something useful for vector and flat associative containers
#include <boost/container/allocator.hpp>

//"adaptive_pool" is a node allocator, specially suited for
//node-based containers
#include <boost/container/adaptive_pool.hpp>

int main ()
{
   using namespace boost::container;

   //A vector that can reallocate memory to implement faster insertions
   vector<int, allocator<int> > extended_alloc_vector;

   //A flat set that can reallocate memory to implement faster insertions
   flat_set<int, std::less<int>, allocator<int> > extended_alloc_flat_set;

   //A list that can manages nodes to implement faster
   //range insertions and deletions
   list<int, adaptive_pool<int> > extended_alloc_list;

   //A set that can recycle nodes to implement faster
   //range insertions and deletions
   set<int, std::less<int>, adaptive_pool<int> > extended_alloc_set;

   //Now user them as always
   extended_alloc_vector.push_back(0);
   extended_alloc_flat_set.insert(0);
   extended_alloc_list.push_back(0);
   extended_alloc_set.insert(0);

   //...
   return 0;
}