The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference
by Nicolai M. Josuttis, Addison-Wesley, 1999
© Copyright Nicolai M. Josuttis 1999
namespace std {
template <class T>
class allocator {
public:
// type definitions
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef T* pointer;
typedef const T* const_pointer;
typedef T& reference;
typedef const T& const_reference;
typedef T value_type;
// rebind allocator to type U
template <class U>
struct rebind {
typedef allocator<U> other;
};
// return address of values
pointer address (reference value) const {
return &value;
}
const_pointer address (const_reference value) const {
return &value;
}
/* constructors and destructor
* - nothing to do because the allocator has no state
*/
allocator() throw() {
}
allocator(const allocator&) throw() {
}
template <class U>
allocator (const allocator<U>&) throw() {
}
~allocator() throw() {
}
// return maximum number of elements that can be allocated
size_type max_size () const throw() {
return numeric_limits<size_t>::max() / sizeof(T);
}
// allocate but don't initialize num elements of type T
pointer allocate (size_type num,
allocator<void>::const_pointer hint = 0) {
// allocate memory with global new
return (pointer)(::operator new(num*sizeof(T)));
}
// initialize elements of allocated storage p with value value
void construct (pointer p, const T& value) {
// initialize memory with placement new
new((void*)p)T(value);
}
// destroy elements of initialized storage p
void destroy (pointer p) {
// destroy objects by calling their destructor
p->~T();
}
// deallocate storage p of deleted elements
void deallocate (pointer p, size_type num) {
// deallocate memory with global delete
::operator delete((void*)p);
}
};
// return that all specializations of this allocator are interchangeable
template <class T1, class T2>
bool operator== (const allocator<T1>&,
const allocator<T2>&) throw() {
return true;
}
template <class T1, class T2>
bool operator!= (const allocator<T1>&,
const allocator<T2>&) throw() {
return false;
}
}