I've got an extremely basic allocator:
template<typename T>
struct Allocator : public std::allocator<T> {
inline typename std::allocator<T>::pointer allocate(typename std::allocator<T>::size_type n, typename std::allocator<void>::const_pointer = 0) {
std::cout << "Allocating: " << n << " itens." << std::endl;
return reinterpret_cast<typename std::allocator<T>::pointer>(::operator new(n * sizeof (T)));
}
inline void deallocate(typename std::allocator<T>::pointer p, typename std::allocator<T>::size_type n) {
std::cout << "Dealloc: " << n << " itens." << std::endl;
::operator delete(p);
}
template<typename U>
struct rebind {
typedef Allocator<U> other;
};
};
Which works fine when I use it with: "std::vector >", however, when I try use it with an std::map like:
int main(int, char**) {
std::map<int, int, Allocator< std::pair<const int, int> > > map;
for (int i(0); i < 100; ++i) {
std::cout << "Inserting the " << i << " item. " << std::endl;
map.insert(std::make_pair(i*i, 2*i));
}
return 0;
}
It fails to compile (gcc 4.6) giving an extremely long error ending with: /usr/lib/gcc/x86_64-redhat-linux/4.6.0/../../../../include/c++/4.6.0/bits/stl_tree.h:959:25: error: no match for call to ‘(Allocator<std::pair<const int, int> >) (std::pair<const int, int>::first_type&, const int&)’
Because allocator is 4th template parameter, whereas 3rd parameter is comparator like std::less
?
so std::map<int, int, std::less<int>, Allocator< std::pair<const int, int> > >
should work.
Also I think you should add default ctor and copy ctor:
Allocator() {}
template<class Other>
Allocator( const Allocator<Other>& _Right ) {}
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