The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <cstddef> // for size_t
template <typename T>
class MyAlloc {
public:
// type definitions
typedef T value_type;
// constructors
// - nothing to do because the allocator has no state
MyAlloc () noexcept {
}
template <typename U>
MyAlloc (const MyAlloc<U>&) noexcept {
// no state to copy
}
// allocate but don't initialize num elements of type T
T* allocate (std::size_t num) {
// allocate memory with global new
return static_cast<T*>(::operator new(num*sizeof(T)));
}
// deallocate storage p of deleted elements
void deallocate (T* p, std::size_t num) {
// deallocate memory with global delete
::operator delete(p);
}
};
// return that all specializations of this allocator are interchangeable
template <typename T1, typename T2>
bool operator== (const MyAlloc<T1>&,
const MyAlloc<T2>&) noexcept {
return true;
}
template <typename T1, typename T2>
bool operator!= (const MyAlloc<T1>&,
const MyAlloc<T2>&) noexcept {
return false;
}