std::vector<bool>

 

C++

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

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Tables

Iterator invalidation

Member function table

Non-member function table

 

std::vector<bool>

Member types
vector<bool>::reference
Member functions
vector::vector vector::~vector vector::operator= vector::assign vector::assign_range (C++23) vector::get_allocator Element access vector::operator[] vector::at vector::front vector::back Iterators vector::beginvector::cbegin (C++11) vector::endvector::cend (C++11) vector::rbeginvector::crbegin (C++11) vector::rendvector::crend (C++11)	Capacity vector::empty vector::size vector::max_size vector::capacity vector::resize vector::reserve vector::shrink_to_fit (DR*) Modifiers vector::clear vector::erase vector::insert vector::insert_range (C++23) vector::append_range (C++23) vector::emplace (C++11) vector::emplace_back (C++11) vector::push_back vector::pop_back vector::swap vector<bool>::flip vector<bool>::swap
Non-member functions
operator==operator<=> (C++20) swap(std::vector<bool>) erase(std::vector<bool>)erase_if(std::vector<bool>) (C++20)(C++20)	operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Helper classes
hash<std::vector<bool>> (C++11)
Deduction guides (C++17)

 

Defined in header <vector>
template< class Allocator > class vector<bool, Allocator>;

std::vector<bool> is a possibly space-efficient specialization of std::vector for the type bool.

The manner in which std::vector<bool> is made space efficient (as well as whether it is optimized at all) is implementation defined. One potential optimization involves coalescing vector elements such that each element occupies a single bit instead of sizeof(bool) bytes.

std::vector<bool> behaves similarly to std::vector, but in order to be space efficient, it:

• Does not necessarily store its elements as a contiguous array.
• Exposes class std::vector<bool>::reference as a method of accessing individual bits. In particular, objects of this class are returned by operator[] by value.
• Does not use std::allocator_traits::construct to construct bit values.
• Does not guarantee that different elements in the same container can be modified concurrently by different threads.

Member types

Member type	Definition
value_type	bool
allocator_type	Allocator
size_type	implementation-defined
difference_type	implementation-defined
reference	proxy class representing a reference to a single bool (class)
const_reference	bool
pointer	implementation-defined
const_pointer	implementation-defined
iterator	implementation-defined (until C++20) implementation-defined ConstexprIterator (since C++20)
const_iterator	implementation-defined (until C++20) implementation-defined ConstexprIterator (since C++20)
reverse_iterator	std::reverse_iterator<iterator>
const_reverse_iterator	std::reverse_iterator<const_iterator>

Member functions

(constructor)	constructs the vector (public member function of std::vector<T,Allocator>)
(destructor)	destructs the vector (public member function of std::vector<T,Allocator>)
operator=	assigns values to the container (public member function of std::vector<T,Allocator>)
assign	assigns values to the container (public member function of std::vector<T,Allocator>)
assign_range (C++23)	assigns a range of values to the container (public member function of std::vector<T,Allocator>)
get_allocator	returns the associated allocator (public member function of std::vector<T,Allocator>)
Element access
at	access specified element with bounds checking (public member function of std::vector<T,Allocator>)
operator[]	access specified element (public member function of std::vector<T,Allocator>)
front	access the first element (public member function of std::vector<T,Allocator>)
back	access the last element (public member function of std::vector<T,Allocator>)
Iterators
begincbegin (C++11)	returns an iterator to the beginning (public member function of std::vector<T,Allocator>)
endcend (C++11)	returns an iterator to the end (public member function of std::vector<T,Allocator>)
rbegincrbegin (C++11)	returns a reverse iterator to the beginning (public member function of std::vector<T,Allocator>)
rendcrend (C++11)	returns a reverse iterator to the end (public member function of std::vector<T,Allocator>)
Capacity
empty	checks whether the container is empty (public member function of std::vector<T,Allocator>)
size	returns the number of elements (public member function of std::vector<T,Allocator>)
max_size	returns the maximum possible number of elements (public member function of std::vector<T,Allocator>)
reserve	reserves storage (public member function of std::vector<T,Allocator>)
capacity	returns the number of elements that can be held in currently allocated storage (public member function of std::vector<T,Allocator>)
Modifiers
clear	clears the contents (public member function of std::vector<T,Allocator>)
insert	inserts elements (public member function of std::vector<T,Allocator>)
insert_range (C++23)	inserts a range of elements (public member function of std::vector<T,Allocator>)
append_range (C++23)	adds a range of elements to the end (public member function of std::vector<T,Allocator>)
emplace (C++11)	constructs element in-place (public member function of std::vector<T,Allocator>)
erase	erases elements (public member function of std::vector<T,Allocator>)
push_back	adds an element to the end (public member function of std::vector<T,Allocator>)
emplace_back (C++11)	constructs an element in-place at the end (public member function of std::vector<T,Allocator>)
pop_back	removes the last element (public member function of std::vector<T,Allocator>)
resize	changes the number of elements stored (public member function of std::vector<T,Allocator>)
swap	swaps the contents (public member function of std::vector<T,Allocator>)
vector<bool> specific modifiers
flip	flips all the bits (public member function)
swap [static]	swaps two std::vector<bool>::references (public static member function)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares the values of two vectors (function template)
std::swap(std::vector)	specializes the std::swap algorithm (function template)
erase(std::vector)erase_if(std::vector) (C++20)	erases all elements satisfying specific criteria (function template)

Helper classes

std::hash<std::vector<bool>> (C++11)

hash support for std::vector<bool> (class template specialization)

Notes

If the size of the bitset is known at compile time, std::bitset may be used, which offers a richer set of member functions. In addition, boost::dynamic_bitset exists as an alternative to std::vector<bool>.

Since its representation may be optimized, std::vector<bool> does not necessarily meet all Container or SequenceContainer requirements. For example, because std::vector<bool>::iterator is implementation-defined, it may not satisfy the LegacyForwardIterator requirement. Use of algorithms such as std::search that require LegacyForwardIterators may result in either compile-time or run-time errors.

The Boost.Container version of vector does not specialize for bool.

Feature-test macro	Value	Std	Feature
__cpp_lib_containers_ranges	202202L	(C++23)	Ranges construction and insertion for containers

Example

Run this code

#include <cassert>
#include <initializer_list>
#include <iostream>
#include <vector>

void println(auto rem, const std::vector<bool>& vb)
{
    std::cout << rem << " = [";
    for (std::size_t t{}; t != vb.size(); ++t)
        std::cout << (t ? ", " : "") << vb[t];
    std::cout << "]\n";
}

int main()
{
    std::vector<bool> v1; // creates an empty vector of boolean values
    println("1) v1", v1);

    std::vector<bool> v2{0, 1, 1, 0, 1}; // creates filled vector
    println("2) v2", v2);

    v1 = v2; // copies v2 to v1
    println("3) v1", v1);

    assert(v1.size() == v2.size()); // checks that v1 and v2 sizes are equal
    assert(v1.front() == false); // accesses first element, equivalent to:
    assert(v1[0] == false);
    assert(v1.back() == true); // accesses last element, equivalent to:
    assert(v1[v1.size() - 1] == true);

    v1 = {true, true, false, false}; // assigns an initializer list
    println("4) v1", v1);

    v1.push_back(true); // adds one element to the end
    println("5) v1", v1);

    v1.pop_back(); // removes one element from the end
    println("6) v1", v1);

    v1.flip(); // flips all elements
    println("7) v1", v1);

    v1.resize(8, true); // resizes v1; new elements are set to “true”
    println("8) v1", v1);

    v1.clear(); // erases v1
    assert(v1.empty()); // checks that v1 is empty
}

Output:

1) v1 = []
2) v2 = [0, 1, 1, 0, 1]
3) v1 = [0, 1, 1, 0, 1]
4) v1 = [1, 1, 0, 0]
5) v1 = [1, 1, 0, 0, 1]
6) v1 = [1, 1, 0, 0]
7) v1 = [0, 0, 1, 1]
8) v1 = [0, 0, 1, 1, 1, 1, 1, 1]

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2187	C++11	specializations for bool lacked emplace and emplace_back member functions	added