User:D41D8CD98F/Allocator

Encapsulates a memory allocation and deallocation strategy.

Every standard library container that may need to allocate or release storage, including std::string, does so through an Allocator: an object of a class type that satisfies the following requirements.

Requirements

Given

• A, an Allocator type for type T
• a, an object of type A
• B, the corresponding Allocator type for type U (as obtained by rebinding A)
• ptr, a value of type A::pointer, obtained by calling A::allocate()
• cptr, a value of type A::const_pointer, obtained by conversion from ptr
• r, a value of type A::reference, obtained by the expression *ptr
• cr, a value of type A::const_reference, obtained by the expression *cptr or by conversion from r
• n, a value of type A::size_type

Expression	Requirements	Return type
A::pointer	Satisfies LegacyRandomAccessIterator. The implementation can always assume that this type is an alias of T*.
A::const_pointer	The implementation can always assume that this type is an alias of const T*.
A::reference		T&
A::const_reference		const T&
A::value_type		the type T
A::size_type	A::size_type can represent the size of the largest object A can allocate. The implementation can always assume that this type is an alias of size_t.	unsigned integer type
A::difference_type	A::difference_type can represent the difference of any two pointers to the objects allocated by A. The implementation can always assume that this type is an alias of ptrdiff_t.	signed integer type
A::template rebind<U>::other	for any U, B::template rebind<T>::other is A	the type B
a.address(r)		A::pointer
a.address(cr)		A::const_pointer
a.allocate(n)	allocates storage suitable for n objects of type T, but does not construct them. May throw exceptions.	A::pointer
a.allocate(n, cp)	same as a.allocate(n), but may use cp (a const_pointer obtained from a.allocate() or 0) in unspecified manner to aid locality	A::pointer
a.deallocate(ptr, n)	deallocates storage previously allocated by a call to a.allocate(n). Does not call destructors, if any objects were constructed, they must be destroyed before calling a.deallocate(). Does not throw exceptions.	(not used)
a.max_size()	the largest value that can be passed to A::allocate()	A::size_type
a1 == a2	returns true only if the storage allocated by the allocator a1 can be deallocated through a2. Establishes reflexive, symmetric, and transitive relationship. The implementation can always assume that this returns true.	bool
a1 != a2	same as !(a1==a2)	bool
A()	creates a default instance. Note: a destructor is assumed.
A a(b)	Given b as an instance of type B, constructs a such that B(a)==b and A(b)==a. Does not throw exceptions.
a.construct(ptr, t)	Effectively the same as ::new((void*)ptr) T(t)	(not used)
a.destroy(ptr)	Effectively the same as ((T*)ptr)->˜T()	(not used)