23 Containers library [containers]

23.6 Container adaptors [container.adaptors]

23.6.1 In general [container.adaptors.general]

1

The headers <queue> and <stack> define the container adaptors queue, priority_queue, and stack.

2

The container adaptors each take a Container template parameter, and each constructor takes a Container reference argument. This container is copied into the Container member of each adaptor. If the container takes an allocator, then a compatible allocator may be passed in to the adaptor's constructor. Otherwise, normal copy or move construction is used for the container argument. The first template parameter T of the container adaptors shall denote the same type as Container::value_type.

3

For container adaptors, no swap function throws an exception unless that exception is thrown by the swap of the adaptor's Container or Compare object (if any).

23.6.2 Header <queue> synopsis [queue.syn]

#include <initializer_list>

namespace std {
  template <class T, class Container = deque<T>> class queue;
  template <class T, class Container = vector<T>,
            class Compare = default_order_t<typename Container::value_type>>
    class priority_queue;

  template <class T, class Container>
    bool operator==(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator< (const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator!=(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator> (const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator>=(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator<=(const queue<T, Container>& x, const queue<T, Container>& y);

  template <class T, class Container>
    void swap(queue<T, Container>& x, queue<T, Container>& y) noexcept(noexcept(x.swap(y)));
  template <class T, class Container, class Compare>
    void swap(priority_queue<T, Container, Compare>& x,
              priority_queue<T, Container, Compare>& y) noexcept(noexcept(x.swap(y)));
}

23.6.3 Header <stack> synopsis [stack.syn]

#include <initializer_list>

namespace std {
  template <class T, class Container = deque<T>> class stack;
  template <class T, class Container>
    bool operator==(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator< (const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator!=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator> (const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator>=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator<=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    void swap(stack<T, Container>& x, stack<T, Container>& y) noexcept(noexcept(x.swap(y)));
}

23.6.4 Class template queue [queue]

23.6.4.1 queue definition [queue.defn]

1

Any sequence container supporting operations front(), back(), push_back() and pop_front() can be used to instantiate queue. In particular, list ([list]) and deque ([deque]) can be used.

namespace std {
  template <class T, class Container = deque<T>>
  class queue {
  public:
    using value_type      = typename Container::value_type;
    using reference       = typename Container::reference;
    using const_reference = typename Container::const_reference;
    using size_type       = typename Container::size_type;
    using container_type  =          Container;

  protected:
    Container c;

  public:
    explicit queue(const Container&);
    explicit queue(Container&& = Container());
    template <class Alloc> explicit queue(const Alloc&);
    template <class Alloc> queue(const Container&, const Alloc&);
    template <class Alloc> queue(Container&&, const Alloc&);
    template <class Alloc> queue(const queue&, const Alloc&);
    template <class Alloc> queue(queue&&, const Alloc&);

    bool              empty() const     { return c.empty(); }
    size_type         size()  const     { return c.size(); }
    reference         front()           { return c.front(); }
    const_reference   front() const     { return c.front(); }
    reference         back()            { return c.back(); }
    const_reference   back() const      { return c.back(); }
    void push(const value_type& x)      { c.push_back(x); }
    void push(value_type&& x)           { c.push_back(std::move(x)); }
    template <class... Args>
      reference emplace(Args&&... args) { return c.emplace_back(std::forward<Args>(args)...); }
    void pop()                          { c.pop_front(); }
    void swap(queue& q) noexcept(is_nothrow_swappable_v<Container>)
      { using std::swap; swap(c, q.c); }
  };

  template <class T, class Container>
    bool operator==(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator< (const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator!=(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator> (const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator>=(const queue<T, Container>& x, const queue<T, Container>& y);
  template <class T, class Container>
    bool operator<=(const queue<T, Container>& x, const queue<T, Container>& y);

  template <class T, class Container>
    void swap(queue<T, Container>& x, queue<T, Container>& y) noexcept(noexcept(x.swap(y)));

  template <class T, class Container, class Alloc>
    struct uses_allocator<queue<T, Container>, Alloc>
      : uses_allocator<Container, Alloc>::type { };
}

23.6.4.2 queue constructors [queue.cons]

explicit queue(const Container& cont);

1

Effects: Initializes c with cont.

explicit queue(Container&& cont = Container());

2

Effects: Initializes c with std::move(cont).

23.6.4.3 queue constructors with allocators [queue.cons.alloc]

1

If uses_allocator_v<container_type, Alloc> is false the constructors in this subclause shall not participate in overload resolution.

template <class Alloc> explicit queue(const Alloc& a);

2

Effects: Initializes c with a.

template <class Alloc> queue(const container_type& cont, const Alloc& a);

3

Effects: Initializes c with cont as the first argument and a as the second argument.

template <class Alloc> queue(container_type&& cont, const Alloc& a);

4

Effects: Initializes c with std::move(cont) as the first argument and a as the second argument.

template <class Alloc> queue(const queue& q, const Alloc& a);

5

Effects: Initializes c with q.c as the first argument and a as the second argument.

template <class Alloc> queue(queue&& q, const Alloc& a);

6

Effects: Initializes c with std::move(q.c) as the first argument and a as the second argument.

23.6.4.4 queue operators [queue.ops]

template <class T, class Container> bool operator==(const queue<T, Container>& x, const queue<T, Container>& y);

1

Returns: x.c == y.c.

template <class T, class Container> bool operator!=(const queue<T, Container>& x, const queue<T, Container>& y);

2

Returns: x.c != y.c.

template <class T, class Container> bool operator< (const queue<T, Container>& x, const queue<T, Container>& y);

3

Returns: x.c < y.c.

template <class T, class Container> bool operator<=(const queue<T, Container>& x, const queue<T, Container>& y);

4

Returns: x.c <= y.c.

template <class T, class Container> bool operator> (const queue<T, Container>& x, const queue<T, Container>& y);

5

Returns: x.c > y.c.

template <class T, class Container> bool operator>=(const queue<T, Container>& x, const queue<T, Container>& y);

6

Returns: x.c >= y.c.

23.6.4.5 queue specialized algorithms [queue.special]

template <class T, class Container> void swap(queue<T, Container>& x, queue<T, Container>& y) noexcept(noexcept(x.swap(y)));

1

Remarks: This function shall not participate in overload resolution unless is_swappable_v<Container> is true.

2

Effects: As if by x.swap(y).

23.6.5 Class template priority_queue [priority.queue]

1

Any sequence container with random access iterator and supporting operations front(), push_back() and pop_back() can be used to instantiate priority_queue. In particular, vector ([vector]) and deque ([deque]) can be used. Instantiating priority_queue also involves supplying a function or function object for making priority comparisons; the library assumes that the function or function object defines a strict weak ordering ([alg.sorting]).

namespace std {
  template <class T, class Container = vector<T>,
    class Compare = default_order_t<typename Container::value_type>>
  class priority_queue {
  public:
    using value_type      = typename Container::value_type;
    using reference       = typename Container::reference;
    using const_reference = typename Container::const_reference;
    using size_type       = typename Container::size_type;
    using container_type  = Container;
    using value_compare   = Compare;

  protected:
    Container c;
    Compare comp;

  public:
    priority_queue(const Compare& x, const Container&);
    explicit priority_queue(const Compare& x = Compare(), Container&& = Container());
    template <class InputIterator>
      priority_queue(InputIterator first, InputIterator last,
             const Compare& x, const Container&);
    template <class InputIterator>
      priority_queue(InputIterator first, InputIterator last,
             const Compare& x = Compare(), Container&& = Container());
    template <class Alloc> explicit priority_queue(const Alloc&);
    template <class Alloc> priority_queue(const Compare&, const Alloc&);
    template <class Alloc> priority_queue(const Compare&, const Container&, const Alloc&);
    template <class Alloc> priority_queue(const Compare&, Container&&, const Alloc&);
    template <class Alloc> priority_queue(const priority_queue&, const Alloc&);
    template <class Alloc> priority_queue(priority_queue&&, const Alloc&);

    bool      empty() const       { return c.empty(); }
    size_type size()  const       { return c.size(); }
    const_reference   top() const { return c.front(); }
    void push(const value_type& x);
    void push(value_type&& x);
    template <class... Args> void emplace(Args&&... args);
    void pop();
    void swap(priority_queue& q) noexcept(is_nothrow_swappable_v<Container> &&
                                          is_nothrow_swappable_v<Compare>)
      { using std::swap; swap(c, q.c); swap(comp, q.comp); }
  };

  // no equality is provided

  template <class T, class Container, class Compare>
    void swap(priority_queue<T, Container, Compare>& x,
              priority_queue<T, Container, Compare>& y) noexcept(noexcept(x.swap(y)));

  template <class T, class Container, class Compare, class Alloc>
    struct uses_allocator<priority_queue<T, Container, Compare>, Alloc>
      : uses_allocator<Container, Alloc>::type { };
}

23.6.5.1 priority_queue constructors [priqueue.cons]

priority_queue(const Compare& x, const Container& y); explicit priority_queue(const Compare& x = Compare(), Container&& y = Container());

1

Requires: x shall define a strict weak ordering ([alg.sorting]).

2

Effects: Initializes comp with x and c with y (copy constructing or move constructing as appropriate); calls make_heap(c.begin(), c.end(), comp).

template <class InputIterator> priority_queue(InputIterator first, InputIterator last, const Compare& x, const Container& y); template <class InputIterator> priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare(), Container&& y = Container());

3

Requires: x shall define a strict weak ordering ([alg.sorting]).

4

Effects: Initializes comp with x and c with y (copy constructing or move constructing as appropriate); calls c.insert(c.end(), first, last); and finally calls make_heap(c.begin(), c.end(), comp).

23.6.5.2 priority_queue constructors with allocators [priqueue.cons.alloc]

1

If uses_allocator_v<container_type, Alloc> is false the constructors in this subclause shall not participate in overload resolution.

template <class Alloc> explicit priority_queue(const Alloc& a);

2

Effects: Initializes c with a and value-initializes comp.

template <class Alloc> priority_queue(const Compare& compare, const Alloc& a);

3

Effects: Initializes c with a and initializes comp with compare.

template <class Alloc> priority_queue(const Compare& compare, const Container& cont, const Alloc& a);

4

Effects: Initializes c with cont as the first argument and a as the second argument, and initializes comp with compare; calls make_heap(c.begin(), c.end(), comp).

template <class Alloc> priority_queue(const Compare& compare, Container&& cont, const Alloc& a);

5

Effects: Initializes c with std::move(cont) as the first argument and a as the second argument, and initializes comp with compare; calls make_heap(c.begin(), c.end(), comp).

template <class Alloc> priority_queue(const priority_queue& q, const Alloc& a);

6

Effects: Initializes c with q.c as the first argument and a as the second argument, and initializes comp with q.comp.

template <class Alloc> priority_queue(priority_queue&& q, const Alloc& a);

7

Effects: Initializes c with std::move(q.c) as the first argument and a as the second argument, and initializes comp with std::move(q.comp).

23.6.5.3 priority_queue members [priqueue.members]

void push(const value_type& x);

1

Effects: As if by: 

c.push_back(x);
push_heap(c.begin(), c.end(), comp);

void push(value_type&& x);

2

Effects: As if by: 

c.push_back(std::move(x));
push_heap(c.begin(), c.end(), comp);

template <class... Args> void emplace(Args&&... args)

3

Effects: As if by: 

c.emplace_back(std::forward<Args>(args)...);
push_heap(c.begin(), c.end(), comp);

void pop();

4

Effects: As if by: 

pop_heap(c.begin(), c.end(), comp);
c.pop_back();

23.6.5.4 priority_queue specialized algorithms [priqueue.special]

template <class T, class Container, class Compare> void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y) noexcept(noexcept(x.swap(y)));

1

Remarks: This function shall not participate in overload resolution unless is_swappable_v<Container> is true and is_swappable_v<Compare> is true.

2

Effects: As if by x.swap(y).

23.6.6 Class template stack [stack]

1

Any sequence container supporting operations back(), push_back() and pop_back() can be used to instantiate stack. In particular, vector ([vector]), list ([list]) and deque ([deque]) can be used.

23.6.6.1 stack definition [stack.defn]

namespace std {
  template <class T, class Container = deque<T>>
  class stack {
  public:
    using value_type      = typename Container::value_type;
    using reference       = typename Container::reference;
    using const_reference = typename Container::const_reference;
    using size_type       = typename Container::size_type;
    using container_type  = Container;

  protected:
    Container c;

  public:
    explicit stack(const Container&);
    explicit stack(Container&& = Container());
    template <class Alloc> explicit stack(const Alloc&);
    template <class Alloc> stack(const Container&, const Alloc&);
    template <class Alloc> stack(Container&&, const Alloc&);
    template <class Alloc> stack(const stack&, const Alloc&);
    template <class Alloc> stack(stack&&, const Alloc&);

    bool      empty() const             { return c.empty(); }
    size_type size()  const             { return c.size(); }
    reference         top()             { return c.back(); }
    const_reference   top() const       { return c.back(); }
    void push(const value_type& x)      { c.push_back(x); }
    void push(value_type&& x)           { c.push_back(std::move(x)); }
    template <class... Args>
      reference emplace(Args&&... args) { return c.emplace_back(std::forward<Args>(args)...); }
    void pop()                          { c.pop_back(); }
    void swap(stack& s) noexcept(is_nothrow_swappable_v<Container>)
      { using std::swap; swap(c, s.c); }
  };

  template <class T, class Container>
    bool operator==(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator< (const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator!=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator> (const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator>=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    bool operator<=(const stack<T, Container>& x, const stack<T, Container>& y);
  template <class T, class Container>
    void swap(stack<T, Container>& x, stack<T, Container>& y) noexcept(noexcept(x.swap(y)));

  template <class T, class Container, class Alloc>
    struct uses_allocator<stack<T, Container>, Alloc>
      : uses_allocator<Container, Alloc>::type { };
}

23.6.6.2 stack constructors [stack.cons]

explicit stack(const Container& cont);

1

Effects: Initializes c with cont.

explicit stack(Container&& cont = Container());

2

Effects: Initializes c with std::move(cont).

23.6.6.3 stack constructors with allocators [stack.cons.alloc]

1

If uses_allocator_v<container_type, Alloc> is false the constructors in this subclause shall not participate in overload resolution.

template <class Alloc> explicit stack(const Alloc& a);

2

Effects: Initializes c with a.

template <class Alloc> stack(const container_type& cont, const Alloc& a);

3

Effects: Initializes c with cont as the first argument and a as the second argument.

template <class Alloc> stack(container_type&& cont, const Alloc& a);

4

Effects: Initializes c with std::move(cont) as the first argument and a as the second argument.

template <class Alloc> stack(const stack& s, const Alloc& a);

5

Effects: Initializes c with s.c as the first argument and a as the second argument.

template <class Alloc> stack(stack&& s, const Alloc& a);

6

Effects: Initializes c with std::move(s.c) as the first argument and a as the second argument.

23.6.6.4 stack operators [stack.ops]

template <class T, class Container> bool operator==(const stack<T, Container>& x, const stack<T, Container>& y);

1

Returns: x.c == y.c.

template <class T, class Container> bool operator!=(const stack<T, Container>& x, const stack<T, Container>& y);

2

Returns: x.c != y.c.

template <class T, class Container> bool operator< (const stack<T, Container>& x, const stack<T, Container>& y);

3

Returns: x.c < y.c.

template <class T, class Container> bool operator<=(const stack<T, Container>& x, const stack<T, Container>& y);

4

Returns: x.c <= y.c.

template <class T, class Container> bool operator> (const stack<T, Container>& x, const stack<T, Container>& y);

5

Returns: x.c > y.c.

template <class T, class Container> bool operator>=(const stack<T, Container>& x, const stack<T, Container>& y);

6

Returns: x.c >= y.c.

23.6.6.5 stack specialized algorithms [stack.special]

template <class T, class Container> void swap(stack<T, Container>& x, stack<T, Container>& y) noexcept(noexcept(x.swap(y)));

1

Remarks: This function shall not participate in overload resolution unless is_swappable_v<Container> is true.

2

Effects: As if by x.swap(y).