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

The manner in whichstd::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 ofsizeof(bool) bytes.

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

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

[edit]Member types

[edit]Member functions

[edit]Non-member functions

[edit]Helper classes

[edit]Deduction guides(C++17)

[edit]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 tostd::vector<bool>.

Since its representation may be optimized,std::vector<bool> does not necessarily meet allContainer orSequenceContainer requirements. For example, becausestd::vector<bool>::iterator is implementation-defined, it may not satisfy theLegacyForwardIterator requirement. Use of algorithms such asstd::search that requireLegacyForwardIterators may result ineither compile-time or run-time errors.

TheBoost.Container version ofvector does not specialize forbool.

[edit]Example

#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}

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]

[edit]Defect reports

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

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