allocator_traits Class

The class template describes an object that supplements an allocator type. An allocator type is any type that describes an allocator object that is used for managing allocated storage. Specifically, for any allocator type Alloc, you can use allocator_traits<Alloc> to determine all the information that is needed by an allocator-enabled container. For more information, see the default allocator Class.

Syntax

template <class Alloc>
    class allocator_traits;

Members

Typedefs

Name	Description
allocator_type	This type is a synonym for the template parameter Alloc.
const_pointer	This type is Alloc::const_pointer, if that type is well-formed; otherwise, this type is pointer_traits<pointer>::rebind<const value_type>.
const_void_pointer	This type is Alloc::const_void_pointer, if that type is well-formed; otherwise, this type is pointer_traits<pointer>::rebind<const void>.
difference_type	This type is Alloc::difference_type, if that type is well-formed; otherwise, this type is pointer_traits<pointer>::difference_type.
pointer	This type is Alloc::pointer, if that type is well-formed; otherwise, this type is value_type *.
propagate_on_container_copy_assignment	This type is Alloc::propagate_on_container_copy_assignment, if that type is well-formed; otherwise, this type is false_type.
propagate_on_container_move_assignment	This type is Alloc::propagate_on_container_move_assignment, if that type is well-formed; otherwise, this type is false_type. If the type holds true, an allocator-enabled container copies its stored allocator on a move assignment.
propagate_on_container_swap	This type is Alloc::propagate_on_container_swap, if that type is well-formed; otherwise, this type is false_type. If the type holds true, an allocator-enabled container swaps its stored allocator on a swap.
size_type	This type is Alloc::size_type, if that type is well-formed; otherwise, this type is make_unsigned<difference_type>::type.
value_type	This type is a synonym for Alloc::value_type.
void_pointer	This type is Alloc::void_pointer, if that type is well-formed; otherwise, this type is pointer_traits<pointer>::rebind<void>.

Static Methods

The following static methods call the corresponding method on a given allocator parameter.

Name	Description
allocate	Static method that allocates memory by using the given allocator parameter.
construct	Static method that uses a specified allocator to construct an object.
deallocate	Static method that uses a specified allocator to deallocate a specified number of objects.
destroy	Static method that uses a specified allocator to call the destructor on an object without deallocating its memory.
max_size	Static method that uses a specified allocator to determine the maximum number of objects that can be allocated.
select_on_container_copy_construction	Static method that calls select_on_container_copy_construction on the specified allocator.

allocate

Static method that allocates memory by using the given allocator parameter.

static pointer allocate(Alloc& al, size_type count);

static pointer allocate(Alloc& al, size_type count,
    typename allocator_traits<void>::const_pointer* hint);

Parameters

al
An allocator object.

count
The number of elements to allocate.

hint
A const_pointer that might assist the allocator object in satisfying the request for storage by locating the address of an allocated object prior to the request. A null pointer is treated as no hint.

Return Value

Each method returns a pointer to the allocated object.

The first static method returns al.allocate(count).

The second method returns al.allocate(count, hint), if that expression is well formed; otherwise it returns al.allocate(count).

construct

Static method that uses a specified allocator to construct an object.

template <class Uty, class Types>
static void construct(Alloc& al, Uty* ptr, Types&&... args);

Parameters

al
An allocator object.

ptr
A pointer to the location where the object is to be constructed.

args
A list of arguments that is passed to the object constructor.

Remarks

The static member function calls al.construct(ptr, args...), if that expression is well formed; otherwise it evaluates ::new (static_cast<void *>(ptr)) Uty(std::forward<Types>(args)...).

deallocate

Static method that uses a specified allocator to deallocate a specified number of objects.

static void deallocate(Alloc al,
    pointer ptr,
    size_type count);

Parameters

al
An allocator object.

ptr
A pointer to the starting location of the objects to be deallocated.

count
The number of objects to deallocate.

Remarks

This method calls al.deallocate(ptr, count).

This method throws nothing.

destroy

Static method that uses a specified allocator to call the destructor on an object without deallocating its memory.

template <class Uty>
    static void destroy(Alloc& al, Uty* ptr);

Parameters

al
An allocator object.

ptr
A pointer to the location of the object.

Remarks

This method calls al.destroy(ptr), if that expression is well formed; otherwise it evaluates ptr->~Uty().

max_size

Static method that uses a specified allocator to determine the maximum number of objects that can be allocated.

static size_type max_size(const Alloc& al);

Parameters

al
An allocator object.

Remarks

This method returns al.max_size(), if that expression is well formed; otherwise it returns numeric_limits<size_type>::max().

select_on_container_copy_construction

Static method that calls select_on_container_copy_construction on the specified allocator.

static Alloc select_on_container_copy_construction(const Alloc& al);

Parameters

al
An allocator object.

Return Value

This method returns al.select_on_container_copy_construction(), if that type is well formed; otherwise it returns al.

Remarks

This method is used to specify an allocator when the associated container is copy-constructed.