Allocators

ALLOCATORS:

In C++ computer programming, allocators are an important component of the C++ Standard Library. The standard library provides several data structures, such as list and set, commonly referred to as containers. A common trait among these containers is their ability to change size during the execution of the program. It encapsulates a memory allocation and deallocation strategy.

Every standard library component that may need to allocate or release storage, from std::string, std::vector, and every container except std::array, to std::shared_ptr and std::function, does so through an Allocator: an object of a class type that satisfies the following requirements.

Requirements

·        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 allocator_traits<A>::pointer, obtained by calling allocator_traits<A>::allocate()

·        cptr, a value of type allocator_traits<A>::const_pointer, obtained by conversion from ptr

·        vptr, a value of type allocator_traits<A>::void_pointer, obtained by conversion from ptr

·        cvptr, a value of type allocator_traits<A>::const_void_pointer, obtained by conversion from cptr or from vptr

·        xptr, a dereferencable pointer to some type X

Some requirements are optional: the template std::allocator_traits supplies the default implementations for all optional requirements, and all standard library containers and other allocator-aware classes access the allocator through , not directly.