std::polymorphic<T, Allocator>:: valueless_after_move

From cppreference.net

( exposition only* )

allocator
allocator_traits (C++11)
allocation_result (C++23)
scoped_allocator_adaptor (C++11)
pmr::polymorphic_allocator (C++17)

allocator_arg (C++11)
uses_allocator (C++11)
uses_allocator_construction_args (C++20)
make_obj_using_allocator (C++20)
uninitialized_construct_using_allocator (C++20)

Uninitialized memory algorithms

uninitialized_copy
uninitialized_fill
uninitialized_move (C++17)
uninitialized_copy_n (C++11)
uninitialized_fill_n
uninitialized_move_n (C++17)
construct_at (C++20)

uninitialized_default_construct (C++17)
uninitialized_value_construct (C++17)
destroy (C++17)
uninitialized_default_construct_n (C++17)
uninitialized_value_construct_n (C++17)
destroy_n (C++17)
destroy_at (C++17)

Constrained uninitialized memory algorithms

ranges::uninitialized_copy (C++20)
ranges::uninitialized_fill (C++20)
ranges::uninitialized_move (C++20)
ranges::uninitialized_copy_n (C++20)
ranges::uninitialized_fill_n (C++20)
ranges::uninitialized_move_n (C++20)
ranges::construct_at (C++20)

ranges::uninitialized_default_construct (C++20)
ranges::uninitialized_value_construct (C++20)
ranges::destroy (C++20)
ranges::uninitialized_default_construct_n (C++20)
ranges::uninitialized_value_construct_n (C++20)
ranges::destroy_n (C++20)
ranges::destroy_at (C++20)

Memory resources

pmr::memory_resource (C++17)
pmr::get_default_resource (C++17)
pmr::set_default_resource (C++17)
pmr::new_delete_resource (C++17)
pmr::pool_options (C++17)

pmr::null_memory_resource (C++17)
pmr::synchronized_pool_resource (C++17)
pmr::unsynchronized_pool_resource (C++17)
pmr::monotonic_buffer_resource (C++17)

Explicit lifetime management
start_lifetime_as (C++23)
start_lifetime_as_array (C++23)

Types for composite class design
indirect (C++26)
polymorphic (C++26)

Uninitialized storage (until C++20)

raw_storage_iterator ( until C++20* )
get_temporary_buffer ( until C++20* )

return_temporary_buffer ( until C++20* )

Garbage collector support (until C++23)

declare_reachable (C++11) (until C++23)
declare_no_pointers (C++11) (until C++23)
pointer_safety (C++11) (until C++23)

undeclare_reachable (C++11) (until C++23)
undeclare_no_pointers (C++11) (until C++23)
get_pointer_safety (C++11) (until C++23)

Low level memory
management

operator new operator new[]

operator delete operator delete[]

nothrow_t

nothrow

new_handler

set_new_handler

get_new_handler

(C++11)

bad_alloc

bad_array_new_length

(C++11)

align_val_t

(C++17)

destroying_delete_t

(C++20)

launder

(C++17)

Smart pointers

unique_ptr

(C++11)

shared_ptr

(C++11)

weak_ptr

(C++11)

auto_ptr

( until C++17* )

owner_less

(C++11)

owner_less<void>

(C++17)

owner_hash

(C++26)

owner_equal

(C++26)

enable_shared_from_this

(C++11)

bad_weak_ptr

(C++11)

default_delete

(C++11)

out_ptr_t

(C++23)

inout_ptr_t

(C++23)

Miscellaneous

pointer_traits

(C++11)

to_address

(C++20)

addressof

(C++11)

align

(C++11)

assume_aligned

(C++20)

is_sufficiently_aligned

(C++26)

C Library

malloc
calloc
realloc

free
aligned_alloc (C++17)

constexpr bool valueless_after_move ( ) const noexcept ;		(自 C++26 起)

检查 * this 是否为空值状态。

返回值

true 如果 * this 不包含有效值，否则为 false 。

示例

本节内容不完整
原因：缺少示例

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Technical specifications
Symbols index
External libraries

Member functions
polymorphic::polymorphic
polymorphic::~polymorphic
polymorphic::operator=
Observers
polymorphic::operator-> polymorphic::operator*
polymorphic::valueless_after_move
polymorphic::get_allocator
Modifiers
polymorphic::swap
Non-member functions
swap (std::polymorphic)

cppreference.net

Namespaces

Variants

std::polymorphic<T, Allocator>:: valueless_after_move

返回值

示例