STD::ALLOCATOR_TRAITS(3)

💖 std::allocator_traits< _Alloc > 💖

okay bestie, so this is a page from the Library Functions Manual — yes, THE manual, capital letters and everything — and it's about std::allocator_traits< _Alloc >. Come sit with me, we're gonna make allocators make sense. 🫶

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✨ NAME ✨

std::allocator_traits< _Alloc > — the uniform interface to all allocator types.

Like, one glow-up of an interface that every allocator can walk through. 👑

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🌈 SYNOPSIS 🌈

#include <memory>

Inherited by all of these iconic little guys:

__gnu_cxx::__alloc_traits< _Char_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _CharT_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Node_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Bit_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Tp_alloc_type >,
__gnu_cxx::__alloc_traits< _Map_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Pair_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Key_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Val_alloc_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< _Node_allocator >,
__gnu_cxx::pointer< _Tp_alloc_type >,
__gnu_cxx::__alloc_traits< allocator_type >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::other< _Alloc >,
__gnu_cxx::__alloc_traits< std::allocator< value_type > >, and
__gnu_cxx::__alloc_traits< _Alloc, typename >.

not me listing twenty-something types and still being calm about it 💅

🎀 Public Types 🎀

• typedef _Alloc allocator_type — the allocator type. the whole personality, basically.
• using const_pointer — the allocator's const pointer type.
• using const_void_pointer — the allocator's const void pointer type.
• using difference_type — the allocator's difference type.
• using is_always_equal — whether all instances of the allocator type compare equal.
• using pointer — the allocator's pointer type.
• using propagate_on_container_copy_assignment — how the allocator is propagated on copy assignment.
• using propagate_on_container_move_assignment — how the allocator is propagated on move assignment.
• using propagate_on_container_swap — how the allocator is propagated on swap.
• template<typename _Tp> using rebind_alloc — (that's it, that's the entry, no lil description attached 🫠)
• template<typename _Tp> using rebind_traits — (same, no description given)
• using size_type — the allocator's size type.
• typedef _Alloc::value_type value_type — the allocated type.
• using void_pointer — the allocator's void pointer type.

⭐ Static Public Member Functions ⭐

• static constexpr pointer allocate (_Alloc &__a, size_type __n) — allocate memory.
• static constexpr pointer allocate (_Alloc &__a, size_type __n, const_void_pointer __hint) — allocate memory.
• static constexpr auto allocate_at_least (_Alloc &__a, size_type __n) -> allocation_result< pointer, size_type > — allocate memory, generously.
• template<typename _Tp, typename... _Args> static constexpr void construct (_Alloc &__a, _Tp *__p, _Args &&... __args) noexcept(_S_nothrow_construct< _Tp, _Args... >()) — construct an object of type _Tp.
• static constexpr void deallocate (_Alloc &__a, pointer __p, size_type __n) — deallocate memory.
• template<typename _Tp> static constexpr void destroy (_Alloc &__a, _Tp *__p) noexcept(_S_nothrow_destroy< _Tp >()) — destroy an object of type _Tp.
• static constexpr size_type max_size (const _Alloc &__a) noexcept — the maximum supported allocation size.
• static constexpr _Alloc select_on_container_copy_construction (const _Alloc &__rhs) — obtain an allocator to use when copying a container.

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🦋 Detailed Description 🦋

template<typename _Alloc>
    struct std::allocator_traits< _Alloc >

"Uniform interface to all allocator types."

Since: C++11 ✨ (an elder, but a timeless one)

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🌸 Member Typedef Documentation 🌸

template<typename _Alloc> typedef _Alloc std::allocator_traits< _Alloc >::allocator_type

The allocator type.

template<typename _Alloc> using std::allocator_traits< _Alloc >::const_pointer

The allocator's const pointer type. Alloc::const_pointer if that type exists, otherwise pointer_traits<pointer>::rebind<const value_type>

template<typename _Alloc> using std::allocator_traits< _Alloc >::const_void_pointer

The allocator's const void pointer type. Alloc::const_void_pointer if that type exists, otherwise pointer_traits<pointer>::rebind<const void>

template<typename _Alloc> using std::allocator_traits< _Alloc >::difference_type

The allocator's difference type. Alloc::difference_type if that type exists, otherwise pointer_traits<pointer>::difference_type

template<typename _Alloc> using std::allocator_traits< _Alloc >::is_always_equal

Whether all instances of the allocator type compare equal. Alloc::is_always_equal if that type exists, otherwise is_empty<Alloc>::type

template<typename _Alloc> using std::allocator_traits< _Alloc >::pointer

The allocator's pointer type. Alloc::pointer if that type exists, otherwise value_type*

template<typename _Alloc> using std::allocator_traits< _Alloc >::propagate_on_container_copy_assignment

How the allocator is propagated on copy assignment. Alloc::propagate_on_container_copy_assignment if that type exists, otherwise false_type

template<typename _Alloc> using std::allocator_traits< _Alloc >::propagate_on_container_move_assignment

How the allocator is propagated on move assignment. Alloc::propagate_on_container_move_assignment if that type exists, otherwise false_type

template<typename _Alloc> using std::allocator_traits< _Alloc >::propagate_on_container_swap

How the allocator is propagated on swap. Alloc::propagate_on_container_swap if that type exists, otherwise false_type

template<typename _Alloc> using std::allocator_traits< _Alloc >::size_type

The allocator's size type. Alloc::size_type if that type exists, otherwise make_unsigned<difference_type>::type

template<typename _Alloc> typedef _Alloc::value_type std::allocator_traits< _Alloc >::value_type

The allocated type.

template<typename _Alloc> using std::allocator_traits< _Alloc >::void_pointer

The allocator's void pointer type. Alloc::void_pointer if that type exists, otherwise pointer_traits<pointer>::rebind<void>

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🔥 Member Function Documentation 🔥

template<typename _Alloc> constexpr pointer std::allocator_traits< _Alloc >::allocate (_Alloc & __a, size_type __n) [inline], [static], [nodiscard], [constexpr]

Allocate memory.

Parameters

• __a — an allocator.
• __n — the number of objects to allocate space for.

Calls a.allocate(n)

template<typename _Alloc> constexpr pointer std::allocator_traits< _Alloc >::allocate (_Alloc & __a, size_type __n, const_void_pointer __hint) [inline], [static], [nodiscard], [constexpr]

Allocate memory.

Parameters

• __a — an allocator.
• __n — the number of objects to allocate space for.
• __hint — aid to locality.

Returns

Memory of suitable size and alignment for n objects of type value_type

Returns a.allocate(n, hint) if that expression is well-formed, otherwise returns a.allocate(n)

template<typename _Alloc> constexpr auto std::allocator_traits< _Alloc >::allocate_at_least (_Alloc & __a, size_type __n) -> allocation_result< pointer, size_type > [inline], [static], [nodiscard], [constexpr]

Allocate memory, generously. 💝 (the name literally says generous, we love a self-aware king)

Parameters

• __a — an allocator.
• __n — the minimum number of objects to allocate space for.

Returns

Memory of suitable size and alignment for n or more contiguous objects of type value_type.

Returns a.allocate_at_least(n) if that expression is well-formed, else { a.allocate(n), n }. When an allocator is obliged to reserve more space than required for the cited n objects, it may deliver the extra space to the caller.

template<typename _Alloc> template<typename _Tp, typename... _Args> constexpr void std::allocator_traits< _Alloc >::construct (_Alloc & __a, _Tp * __p, _Args &&... __args) [inline], [static], [constexpr], [noexcept]

Construct an object of type _Tp.

Parameters

• __a — an allocator.
• __p — pointer to memory of suitable size and alignment for Tp
• __args — constructor arguments.

Calls __a.construct(__p, std::forward<Args>(__args)...) if that expression is well-formed, otherwise uses placement-new to construct an object of type _Tp at location __p from the arguments __args...

template<typename _Alloc> constexpr void std::allocator_traits< _Alloc >::deallocate (_Alloc & __a, pointer __p, size_type __n) [inline], [static], [constexpr]

Deallocate memory.

Parameters

• __a — an allocator.
• __p — pointer to the memory to deallocate.
• __n — the number of objects space was allocated for.

Calls a.deallocate(p, n)

template<typename _Alloc> template<typename _Tp> constexpr void std::allocator_traits< _Alloc >::destroy (_Alloc & __a, _Tp * __p) [inline], [static], [constexpr], [noexcept]

Destroy an object of type _Tp.

Parameters

• __a — an allocator.
• __p — pointer to the object to destroy

Calls __a.destroy(__p) if that expression is well-formed, otherwise calls __p->~_Tp()

template<typename _Alloc> constexpr size_type std::allocator_traits< _Alloc >::max_size (const _Alloc & __a) [inline], [static], [constexpr], [noexcept]

The maximum supported allocation size.

Parameters

• __a — an allocator.

Returns

__a.max_size() or numeric_limits<size_type>::max()

Returns __a.max_size() if that expression is well-formed, otherwise returns numeric_limits<size_type>::max()

template<typename _Alloc> constexpr _Alloc std::allocator_traits< _Alloc >::select_on_container_copy_construction (const _Alloc & __rhs) [inline], [static], [constexpr]

Obtain an allocator to use when copying a container.

Parameters

• __rhs — an allocator.

Returns

__rhs.select_on_container_copy_construction() or __rhs

Returns __rhs.select_on_container_copy_construction() if that expression is well-formed, otherwise returns __rhs

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👑 Author 👑

Generated automatically by Doxygen for libstdc++ from the source code.

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and that's the whole page bestie, we ate and left zero crumbs 💅✨

this lil doc came out of the libstdc++ source, auto-generated by Doxygen, and the footer was serving std::alloc...s< _Alloc >(3) — the manual page name, no date on it, so that's all the metadata we got 🎀 💖