std::vector - cppreference.com (original) (raw)

| | | | | ------------------------------------------------------------ | | | | 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.

Contents

• 1 Member types
• 2 Member functions
  • 2.1 Element access
  • 2.2 Iterators
  • 2.3 Capacity
  • 2.4 Modifiers
  • 2.5 vector specific modifiers
• 3 Non-member functions
• 4 Helper classes
• 5 Deduction guides (C++17)
• 6 Notes
• 7 Example
• 8 Defect reports

[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 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.

[edit] Example

#include #include #include #include   void println(auto rem, const std::vector& 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 v1; // creates an empty vector of boolean values println("1) v1", v1);   std::vector 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]

[edit] Defect reports

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