C++ In a Nutshell

Name

allocator class template — Encapsulates memory allocation and deallocation

Synopsis

template <class T>
class allocator {
public:
  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;
  template <class U> struct rebind {
    typedef allocator<U> other;
  };
  allocator(  ) throw(  );
  allocator(const allocator&) throw(  );
  template <class U> allocator(const allocator<U>&) throw(  );
  ~allocator(  ) throw(  );
  pointer address(reference x) const;
  const_pointer address(const_reference x) const;
  pointer allocate(size_type, allocator<void>::const_pointer hint = 0);
  void deallocate(pointer p, size_type n);
  size_type max_size(  ) const throw(  );
  void construct(pointer p, const T& val);
  void destroy(pointer p);
};

The allocator class template encapsulates basic allocation and deallocation functions. The standard containers rely on allocators for memory management and use allocator as the default allocator.

Most programmers do not need to use allocator, which offers few advantages over plain new and delete. However, if you want to write your own container, or provide a custom allocator for the standard containers, you should take the time to understand allocator.

Perhaps the easiest way to understand allocator is to take a look at a trivial implementation in Example 13-30. Note that a library might have a more complicated implementation to handle multithreading, improve performance, ...