std::vector<bool>

 

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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, conststd::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 equalassert(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 v1assert(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