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std::vector<bool>::reference

class reference;

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

The primary use of std::vector<bool>::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>::reference potentially read or write to the entire underlying vector.

Member functions

(constructor)
constructs the reference. Accessible only to std::vector<bool> itself
(public member function)
(destructor)
destroys the reference
(public member function)
operator=
assigns a bool to the referenced bit
(public member function)
operator bool
returns the referenced bit
(public member function)
flip
flips the referenced bit
(public member function)

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

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

Destroys the reference.

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

(1) 
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)
(2) 
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.

Parameters

x - value to assign

Return value

*this

std::vector<bool>::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.

Parameters

(none)

Return value

The referenced bit.

std::vector<bool>::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.

Parameters

(none)

Return value

(none)

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>::reference. The specialization uses std::formatter<bool, CharT> as its underlying formatter 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 objects

The formatter contains a private non-static data member underlying_(exposition only*) of type std::formatter<bool, CharT>.

Member functions

template< class ParseContext >
constexpr typename ParseContext::iterator parse(ParseContext& ctx);
 (1) (since C++23) 
template< class FormatContext >
typename 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);.

Example

See also

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

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