[list] (original) (raw)

22 Containers library [containers]

22.3 Sequence containers [sequences]

22.3.10 Class template list [list]

22.3.10.1 Overview [list.overview]

Alistis a sequence container that supports bidirectional iterators and allows constant time insert and erase operations anywhere within the sequence, with storage management handled automatically.

Unlike vectors and deques, fast random access to list elements is not supported, but many algorithms only need sequential access anyway.

A list meets all of the requirements of a container, of a reversible container (given in two tables in[container.requirements]), of a sequence container, including most of the optional sequence container requirements ([sequence.reqmts]), and of an allocator-aware container (Table 76).

The exceptions are theoperator[]andatmember functions, which are not provided.225

Descriptions are provided here only for operations onlistthat are not described in one of these tables or for operations where there is additional semantic information.

namespace std { template<class T, class Allocator = allocator> class list { public:

using value_type             = T;
using allocator_type         = Allocator;
using pointer                = typename allocator_traits<Allocator>::pointer;
using const_pointer          = typename allocator_traits<Allocator>::const_pointer;
using reference              = value_type&;
using const_reference        = const value_type&;
using size_type              = implementation-defined; 
using difference_type        = implementation-defined; 
using iterator               = implementation-defined; 
using const_iterator         = implementation-defined; 
using reverse_iterator       = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;


list() : list(Allocator()) { }
explicit list(const Allocator&);
explicit list(size_type n, const Allocator& = Allocator());
list(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
  list(InputIterator first, InputIterator last, const Allocator& = Allocator());
list(const list& x);
list(list&& x);
list(const list&, const Allocator&);
list(list&&, const Allocator&);
list(initializer_list<T>, const Allocator& = Allocator());
~list();
list& operator=(const list& x);
list& operator=(list&& x)
  noexcept(allocator_traits<Allocator>::is_always_equal::value);
list& operator=(initializer_list<T>);
template<class InputIterator>
  void assign(InputIterator first, InputIterator last);
void assign(size_type n, const T& t);
void assign(initializer_list<T>);
allocator_type get_allocator() const noexcept;


iterator               begin() noexcept;
const_iterator         begin() const noexcept;
iterator               end() noexcept;
const_iterator         end() const noexcept;
reverse_iterator       rbegin() noexcept;
const_reverse_iterator rbegin() const noexcept;
reverse_iterator       rend() noexcept;
const_reverse_iterator rend() const noexcept;

const_iterator         cbegin() const noexcept;
const_iterator         cend() const noexcept;
const_reverse_iterator crbegin() const noexcept;
const_reverse_iterator crend() const noexcept;


[[nodiscard]] bool empty() const noexcept;
size_type size() const noexcept;
size_type max_size() const noexcept;
void      resize(size_type sz);
void      resize(size_type sz, const T& c);


reference       front();
const_reference front() const;
reference       back();
const_reference back() const;


template<class... Args> reference emplace_front(Args&&... args);
template<class... Args> reference emplace_back(Args&&... args);
void push_front(const T& x);
void push_front(T&& x);
void pop_front();
void push_back(const T& x);
void push_back(T&& x);
void pop_back();

template<class... Args> iterator emplace(const_iterator position, Args&&... args);
iterator insert(const_iterator position, const T& x);
iterator insert(const_iterator position, T&& x);
iterator insert(const_iterator position, size_type n, const T& x);
template<class InputIterator>
  iterator insert(const_iterator position, InputIterator first, InputIterator last);
iterator insert(const_iterator position, initializer_list<T> il);

iterator erase(const_iterator position);
iterator erase(const_iterator position, const_iterator last);
void     swap(list&) noexcept(allocator_traits<Allocator>::is_always_equal::value);
void     clear() noexcept;


void splice(const_iterator position, list& x);
void splice(const_iterator position, list&& x);
void splice(const_iterator position, list& x, const_iterator i);
void splice(const_iterator position, list&& x, const_iterator i);
void splice(const_iterator position, list& x, const_iterator first, const_iterator last);
void splice(const_iterator position, list&& x, const_iterator first, const_iterator last);

size_type remove(const T& value);
template<class Predicate> size_type remove_if(Predicate pred);

size_type unique();
template<class BinaryPredicate>
  size_type unique(BinaryPredicate binary_pred);

void merge(list& x);
void merge(list&& x);
template<class Compare> void merge(list& x, Compare comp);
template<class Compare> void merge(list&& x, Compare comp);

void sort();
template<class Compare> void sort(Compare comp);

void reverse() noexcept;

};

template<class InputIterator, class Allocator = allocator<iter-value-type>> list(InputIterator, InputIterator, Allocator = Allocator()) -> list<iter-value-type, Allocator>;

template<class T, class Allocator> void swap(list<T, Allocator>& x, list<T, Allocator>& y) noexcept(noexcept(x.swap(y))); }

T shall be complete before any member of the resulting specialization of list is referenced.

22.3.10.2 Constructors, copy, and assignment [list.cons]

explicit list(const Allocator&);

Effects:Constructs an empty list, using the specified allocator.

explicit list(size_type n, const Allocator& = Allocator());

Preconditions: T is Cpp17DefaultInsertable into *this.

Effects:Constructs a list withn default-inserted elements using the specified allocator.

list(size_type n, const T& value, const Allocator& = Allocator());

Preconditions: T is Cpp17CopyInsertable into *this.

Effects:Constructs alistwithncopies ofvalue, using the specified allocator.

template<class InputIterator> list(InputIterator first, InputIterator last, const Allocator& = Allocator());

Effects:Constructs alistequal to the range[first, last).

Complexity:Linear indistance(first, last).

22.3.10.3 Capacity [list.capacity]

void resize(size_type sz);

Preconditions: T is Cpp17DefaultInsertable into *this.

Effects:If size() < sz, appends sz - size() default-inserted elements to the sequence.

If sz <= size(), equivalent to:

list::iterator it = begin(); advance(it, sz); erase(it, end());

void resize(size_type sz, const T& c);

Preconditions: T is Cpp17CopyInsertable into *this.

Effects:As if by:

if (sz > size()) insert(end(), sz-size(), c); else if (sz < size()) { iterator i = begin(); advance(i, sz); erase(i, end()); } else ;

22.3.10.4 Modifiers [list.modifiers]

iterator insert(const_iterator position, const T& x); iterator insert(const_iterator position, T&& x); iterator insert(const_iterator position, size_type n, const T& x);template<class InputIterator> iterator insert(const_iterator position, InputIterator first, InputIterator last); iterator insert(const_iterator position, initializer_list<T>);template<class... Args> reference emplace_front(Args&&... args);template<class... Args> reference emplace_back(Args&&... args);template<class... Args> iterator emplace(const_iterator position, Args&&... args);void push_front(const T& x);void push_front(T&& x);void push_back(const T& x);void push_back(T&& x);

Remarks:Does not affect the validity of iterators and references.

If an exception is thrown there are no effects.

Complexity:Insertion of a single element into a list takes constant time and exactly one call to a constructor ofT.

Insertion of multiple elements into a list is linear in the number of elements inserted, and the number of calls to the copy constructor or move constructor of T is exactly equal to the number of elements inserted.

iterator erase(const_iterator position); iterator erase(const_iterator first, const_iterator last);void pop_front();void pop_back();void clear() noexcept;

Effects:Invalidates only the iterators and references to the erased elements.

Complexity:Erasing a single element is a constant time operation with a single call to the destructor ofT.

Erasing a range in a list is linear time in the size of the range and the number of calls to the destructor of typeTis exactly equal to the size of the range.

22.3.10.5 Operations [list.ops]

Since lists allow fast insertion and erasing from the middle of a list, certain operations are provided specifically for them.226

In this subclause, arguments for a template parameter named Predicate or BinaryPredicateshall meet the corresponding requirements in [algorithms.requirements].

For merge and sort, the definitions and requirements in [alg.sorting] apply.

list provides three splice operations that destructively move elements from one list to another.

The behavior of splice operations is undefined if get_­allocator() !=x.get_­allocator().

void splice(const_iterator position, list& x);void splice(const_iterator position, list&& x);

Preconditions: addressof(x) != this is true.

Effects:Inserts the contents ofxbeforepositionandxbecomes empty.

Pointers and references to the moved elements ofxnow refer to those same elements but as members of*this.

Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into*this, not intox.

Complexity:Constant time.

void splice(const_iterator position, list& x, const_iterator i);void splice(const_iterator position, list&& x, const_iterator i);

Preconditions: i is a valid dereferenceable iterator of x.

Effects:Inserts an element pointed to byifrom listxbefore position and removes the element fromx.

The result is unchanged ifposition == iorposition == ++i.

Pointers and references to*icontinue to refer to this same element but as a member of*this.

Iterators to*i(includingiitself) continue to refer to the same element, but now behave as iterators into*this, not intox.

Complexity:Constant time.

void splice(const_iterator position, list& x, const_iterator first, const_iterator last);void splice(const_iterator position, list&& x, const_iterator first, const_iterator last);

Preconditions: [first, last) is a valid range in x.

position is not an iterator in the range [first, last).

Effects:Inserts elements in the range[first, last)beforepositionand removes the elements fromx.

Pointers and references to the moved elements ofxnow refer to those same elements but as members of*this.

Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into*this, not intox.

Complexity:Constant time ifaddressof(x) == this; otherwise, linear time.

size_type remove(const T& value);template<class Predicate> size_type remove_if(Predicate pred);

Effects:Erases all the elements in the list referred to by a list iterator i for which the following conditions hold: *i == value, pred(*i) != false.

Invalidates only the iterators and references to the erased elements.

Returns:The number of elements erased.

Throws:Nothing unless an exception is thrown by*i == valueorpred(*i) != false.

Complexity:Exactlysize()applications of the corresponding predicate.

size_type unique();template<class BinaryPredicate> size_type unique(BinaryPredicate binary_pred);

Effects:Erases all but the first element from every consecutive group of equal elements referred to by the iterator i in the range[first + 1, last) for which *i == *(i-1) (for the version ofunique with no arguments) or pred(*i, *(i - 1)) (for the version ofunique with a predicate argument) holds.

Invalidates only the iterators and references to the erased elements.

Returns:The number of elements erased.

Throws:Nothing unless an exception is thrown by*i == *(i-1)orpred(*i, *(i - 1))

Complexity:If the range[first, last)is not empty, exactly(last - first) - 1applications of the corresponding predicate, otherwise no applications of the predicate.

void merge(list& x);void merge(list&& x);template<class Compare> void merge(list& x, Compare comp);template<class Compare> void merge(list&& x, Compare comp);

Preconditions:Both the list and the argument list shall be sorted with respect to the comparator operator< (for the first two overloads) orcomp (for the last two overloads), andget_­allocator() == x.get_­allocator() is true.

Effects:If addressof(x) == this, does nothing; otherwise, merges the two sorted ranges [begin(), end())and [x.​begin(), x.end()).

The result is a range in which the elements will be sorted in non-decreasing order according to the ordering defined by comp; that is, for every iterator i, in the range other than the first, the conditioncomp(*i, *(i - 1)) will be false.

Pointers and references to the moved elements of x now refer to those same elements but as members of *this.

Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into *this, not intox.

If addressof(x) != this, the range [x.begin(), x.end())is empty after the merge.

No elements are copied by this operation.

Complexity:At mostsize() + x.size() - 1applications of comp ifaddressof(x) != this; otherwise, no applications of comp are performed.

If an exception is thrown other than by a comparison there are no effects.

Effects:Reverses the order of the elements in the list.

Does not affect the validity of iterators and references.

void sort();template<class Compare> void sort(Compare comp);

Effects:Sorts the list according to the operator< or a Compare function object.

If an exception is thrown, the order of the elements in *this is unspecified.

Does not affect the validity of iterators and references.

Complexity:Approximatelycomparisons, whereN == size().

22.3.10.6 Erasure [list.erasure]

template<class T, class Allocator, class U> typename list<T, Allocator>::size_type erase(list<T, Allocator>& c, const U& value);

Effects:Equivalent to: return erase_­if(c, [&](auto& elem) { return elem == value; });

template<class T, class Allocator, class Predicate> typename list<T, Allocator>::size_type erase_if(list<T, Allocator>& c, Predicate pred);

Effects:Equivalent to: return c.remove_­if(pred);