std::vector<bool, Alloc>::reference

class reference;

The std::vector<bool, Alloc> specializations define std::vector<bool, Alloc>::reference as a publicly-accessible nested class. std::vector<bool, Alloc>::reference proxies the behavior of references to a single bit in std::vector<bool, Alloc>.

The primary use of std::vector<bool, Alloc>::reference is to provide an lvalue that can be returned from operator[].

Any reads or writes to a vector that happen via a std::vector<bool, Alloc>::reference potentially read or write to the entire underlying vector.


[edit] Member functions

constructs the reference. Accessible only to std::vector<bool, Alloc> itself
(public member function)
destroys the reference
(public member function)
assigns a bool to the referenced bit
(public member function)
operator bool
returns the referenced bit
(public member function) [edit]
flips the referenced bit
(public member function)

std::vector<bool, Alloc>::reference::~reference

(until C++20)
constexpr ~reference();
(since C++20)

Destroys the reference.

std::vector<bool, Alloc>::reference::operator=

reference& operator=( bool x );
(until C++11)
reference& operator=( bool x ) noexcept;
(since C++11)
(until C++20)
constexpr reference& operator=( bool x ) noexcept;
(since C++20)
reference& operator=( const reference& x );
(until C++11)
reference& operator=( const reference& x ) noexcept;
(since C++11)
(until C++20)
constexpr reference& operator=( const reference& x ) noexcept;
(since C++20)
constexpr const reference& operator=( bool x ) const noexcept;
(3) (since C++23)

Assigns a value to the referenced bit.


x - value to assign

Return value


std::vector<bool, Alloc>::reference::operator bool

operator bool() const;
(until C++11)
operator bool() const noexcept;
(since C++11)
(until C++20)
constexpr operator bool() const noexcept;
(since C++20)

Returns the value of the referenced bit.



Return value

The referenced bit.

std::vector<bool, Alloc>::reference::flip

void flip();
(until C++11)
void flip() noexcept;
(since C++11)
(until C++20)
constexpr void flip() noexcept;
(since C++20)

Inverts the referenced bit.



Return value


[edit] Helper classes

std::formatter<std::vector<bool, Alloc>::reference>

template < class T, class CharT >

  requires /* is-vector-bool-reference */<T>

struct formatter<T, CharT>;
(since C++23)

Specializes the std::formatter for std::vector<bool, Alloc>::reference. The specialization uses std::formatter<bool, CharT> as its underlying formatter (denoted as underlying_) where the referenced bit is converted to bool to be formatted.

The exposition-only constant /* is-vector-bool-reference */<T> is true if and only if T denotes the type std::vector<bool, Alloc>::reference for some type Alloc and std::vector<bool, Alloc> is not a program-defined specialization.

Member functions

template< class ParseContext >
constexpr ParseContext::iterator parse( ParseContext& ctx );
(1) (since C++23)
template< class FormatContext >
FormatContext::iterator format( const T& r, FormatContext& ctx ) const;
(2) (since C++23)
1) Equivalent to return underlying_.parse(ctx);.
2) Equivalent to return underlying_.format(r, ctx);.

[edit] Example

[edit] See also

access specified element
(public member function of std::vector<T,Allocator>) [edit]
swaps two std::vector<bool>::references
(public static member function) [edit]

[edit] External links

"Effective Modern C++" by Scott Meyers (2015), Chapter 2, Item 6: "Use the explicitly typed initializer idiom when auto deduces undesired types." (p.43-46) — describes a possible misuse of the proxy class std::vector<bool>::reference).