c++ - How to completely manage heap memory allocation of std containers like map? -

i'm interested in using multiple std map<int,int> , want of them allocate elements common memory pool. i've read far, can use custom allocators such boost pool_alloc achieve this.

my question is, despite using boost pool_alloc manage allocation of elements themselves, std map still use little bits of heap memory form of container overhead not managed boost pool_alloc? i'm thinking along lines of pointer elements regards use std map itself?

the short version

a map type such as:

typedef std::map<     int,     int,     less<int>,     boost::pool_allocator<pair<const int, int> >     >      amaptype; 

will allocation needs grows using boost::pool_allocators. of initial structure created on stack. how , exact structure though implementation dependent.

allocator rebind

the above possible through use of allocator::rebind

all std::allocator conformant allocators (such boost::pool_allocator) provide rebind template struct in form:

template<class u> struct rebind{    typedef allocatortype<u> other; }; 

this can used obtain same kind of allocator different type:

typedef allocatorofother allocatortype::rebind<adifferenttype>::other; 

gcc std::map internal structure

the g++ std::map implementation (i inspected 4.7.3 , 4.1.1) built purely out of single node type. includes key value pair , pointers , colour bit needed rbtree structure. allocate defines node allocator using rebind struct user provided allocator. used allocations map grows. each new node gets allocated in single allocation.

the standard

i checked though c++11 standard , not find specifying how such structure should allocated. either did not find right part or not specified. not using user given allocator kind seem bit pointless though.