Difference between revisions of "cpp/container/vector bool"
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(LWG 2187, treated ad DR by libc++/libstdc++) |
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The [https://www.boost.org/doc/libs/release/doc/html/boost/container/vector.html Boost.Container version of {{tt|vector}}] does not specialize for {{tt|bool}}. | The [https://www.boost.org/doc/libs/release/doc/html/boost/container/vector.html Boost.Container version of {{tt|vector}}] does not specialize for {{tt|bool}}. | ||
| + | |||
| + | ===Defect reports=== | ||
| + | {{dr list begin}} | ||
| + | {{dr list item|wg=lwg|dr=2187|std=C++11|before=specializations for {{c|bool}} lacked {{tt|emplace}} and {{tt|emplace_back}} member functions|after=added}} | ||
| + | {{dr list end}} | ||
{{langlinks|de|es|fr|it|ja|pt|ru|zh}} | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Revision as of 08:52, 15 January 2022
| Defined in header <vector>
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| template<class Allocator> class vector<bool, Allocator>; |
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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 |
Member types
| Member type | Definition | ||||
value_type
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bool | ||||
allocator_type
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Allocator
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size_type
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implementation-defined | ||||
difference_type
|
implementation-defined | ||||
| proxy class representing a reference to a single bool (class) | |||||
const_reference
|
bool | ||||
pointer
|
implementation-defined | ||||
const_pointer
|
implementation-defined | ||||
iterator
|
| ||||
const_iterator
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| ||||
reverse_iterator
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std::reverse_iterator<iterator> | ||||
const_reverse_iterator
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std::reverse_iterator<const_iterator> |
Member functions
constructs the vector (public member function of std::vector<T,Allocator>)
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destructs the vector (public member function of std::vector<T,Allocator>)
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| assigns values to the container (public member function of std::vector<T,Allocator>)
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| assigns values to the container (public member function of std::vector<T,Allocator>)
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| returns the associated allocator (public member function of std::vector<T,Allocator>)
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Element access | |
| access specified element with bounds checking (public member function of std::vector<T,Allocator>)
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| access specified element (public member function of std::vector<T,Allocator>)
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| access the first element (public member function of std::vector<T,Allocator>)
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| access the last element (public member function of std::vector<T,Allocator>)
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Iterators | |
| (C++11) |
returns an iterator to the beginning (public member function of std::vector<T,Allocator>)
|
| (C++11) |
returns an iterator to the end (public member function of std::vector<T,Allocator>)
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| (C++11) |
returns a reverse iterator to the beginning (public member function of std::vector<T,Allocator>)
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| (C++11) |
returns a reverse iterator to the end (public member function of std::vector<T,Allocator>)
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Capacity | |
| checks whether the container is empty (public member function of std::vector<T,Allocator>)
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| returns the number of elements (public member function of std::vector<T,Allocator>)
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| returns the maximum possible number of elements (public member function of std::vector<T,Allocator>)
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| reserves storage (public member function of std::vector<T,Allocator>)
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| returns the number of elements that can be held in currently allocated storage (public member function of std::vector<T,Allocator>)
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Modifiers | |
| clears the contents (public member function of std::vector<T,Allocator>)
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| inserts elements (public member function of std::vector<T,Allocator>)
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| (C++11) |
constructs element in-place (public member function of std::vector<T,Allocator>)
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| erases elements (public member function of std::vector<T,Allocator>)
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| adds an element to the end (public member function of std::vector<T,Allocator>)
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| (C++11) |
constructs an element in-place at the end (public member function of std::vector<T,Allocator>)
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| removes the last element (public member function of std::vector<T,Allocator>)
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| changes the number of elements stored (public member function of std::vector<T,Allocator>)
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| swaps the contents (public member function of std::vector<T,Allocator>)
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| |
| flips all the bits (public member function) | |
| [static] |
swaps two std::vector<bool>::references (public static member function) |
Non-member functions
| (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) |
| specializes the std::swap algorithm (function template) | |
| erases all elements satisfying specific criteria (function template) |
Helper classes
| (C++11) |
hash support for std::vector<bool> (class template specialization) |
Deduction guides (C++17)
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.
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 |
