Library: General utilities
Does not inherit
The default allocator object for storage management in C++ Standard Library containers
#include <memory>
namespace std {
template <class T>
class allocator;
}
namespace std {
template <> class allocator<void>;
}
Containers in the C++ Standard Library allow you to control storage management through the use of allocator objects. Each container class has an allocator template parameter specifying the type of allocator to be used. Every constructor, except the copy constructor, has an allocator parameter, allowing you to pass in a specific allocator. A container uses that allocator for all storage management.
The library has a default allocator, called allocator. This allocator uses the global new() and delete() operators. By default, all containers use this allocator. You can also design your own allocator, but if you do so it must have an appropriate interface.
namespace std {
template <class T>
class allocator {
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();
template <class U>
allocator& operator=(const allocator<U>&) throw();
~allocator () throw();
pointer address(reference) const;
const_pointer address(const_reference) const;
pointer allocate (size_type,
typename allocator<void>::const_pointer = 0);
void deallocate(pointer p, size_type n);
size_type max_size() const throw();
void construct(pointer, const T&);
void destroy(pointer);
};
// globals
template <class T, class U>
bool operator==(const allocator<T>&,
const allocator<U>&) throw();
template <class T, class U>
bool operator!=(const allocator<T>&,
const allocator<U>&) throw();
}
size_type
Type used to hold the size of an allocated block of storage.
difference_type
Type used to hold values representing distances between storage addresses.
pointer
Type of pointer returned by allocator.
const_pointer
Const version of pointer.
reference
Type of reference to allocated objects.
const_reference
Const version of reference.
value_type
Type of allocated object.
template <class U> struct rebind;
Converts an allocator templatized on one type to an allocator templatized on another type. This struct contains a single type member:
typedef allocator<U> other
allocator()
Default constructor.
template <class U> allocator(const allocator<U>&)
Copy constructor.
~allocator()
Destructor.
pointer address(reference x) const;
Returns the address of the reference x as a pointer.
const_pointer address(const_reference x) const;
Returns the address of the reference x as a const_pointer.
pointer
allocate(size_type n,
typename allocator<void>::const_pointer p = 0)
Allocates storage. Returns a pointer to the first element in a block of storage n*sizeof(T) bytes in size. The block is aligned appropriately for objects of type T. Throws the exception bad_alloc if the storage is unavailable. This function uses operator new(size_t). The second parameter p can be used by an allocator to localize memory allocation, but the default allocator does not use it.
void deallocate(pointer p, size_type n)
Deallocates the storage obtained by a call to allocate() with arguments n and p.
size_type max_size() const;
Returns the largest size for which a call to allocate() might succeed.
void construct(pointer p, const T& val);
Constructs an object of type T2 with the initial value of val at the location specified by p. This function calls the placement new() operator.
void destroy(pointer p)
Calls the destructor on the object pointed to by p, but does not delete.
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.4.1