# std::vector<bool>::reference

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< cpp‎ | container‎ | vector bool

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)

### Example

| This section is incomplete Reason: no example

### See also

operator[] | access specified element (public member function of `std::vector<T,Allocator>`)
swap [static] | swaps two `std::vector<bool>::``reference`s (public static member function)

### 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`).

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