22 Containers library [containers]

22.6 Container adaptors [container.adaptors]

22.6.6 Class template stack [stack]

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

22.6.6.1 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:
    stack() : stack(Container()) {}
    explicit stack(const Container&);
    explicit stack(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&);

    [[nodiscard]] 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>
      decltype(auto) 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 Container>
    stack(Container) -> stack<typename Container::value_type, Container>;

  template<class Container, class Allocator>
    stack(Container, Allocator) -> stack<typename Container::value_type, Container>;

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

22.6.6.2 Constructors [stack.cons]

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explicit stack(const Container& cont);
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Effects: Initializes c with cont.
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explicit stack(Container&& cont);
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Effects: Initializes c with std​::​move(cont).

22.6.6.3 Constructors with allocators [stack.cons.alloc]

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If uses_­allocator_­v<container_­type, Alloc> is false the constructors in this subclause shall not participate in overload resolution.
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template<class Alloc> explicit stack(const Alloc& a);
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Effects: Initializes c with a.
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template<class Alloc> stack(const container_type& cont, const Alloc& a);
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Effects: Initializes c with cont as the first argument and a as the second argument.
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template<class Alloc> stack(container_type&& cont, const Alloc& a);
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Effects: Initializes c with std​::​move(cont) as the first argument and a as the second argument.
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template<class Alloc> stack(const stack& s, const Alloc& a);
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Effects: Initializes c with s.c as the first argument and a as the second argument.
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template<class Alloc> stack(stack&& s, const Alloc& a);
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Effects: Initializes c with std​::​move(s.c) as the first argument and a as the second argument.

22.6.6.4 Operators [stack.ops]

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template<class T, class Container> bool operator==(const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c == y.c.
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template<class T, class Container> bool operator!=(const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c != y.c.
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template<class T, class Container> bool operator< (const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c < y.c.
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template<class T, class Container> bool operator> (const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c > y.c.
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template<class T, class Container> bool operator<=(const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c <= y.c.
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template<class T, class Container> bool operator>=(const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c >= y.c.
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template<class T, three_­way_­comparable Container> compare_three_way_result_t<Container> operator<=>(const stack<T, Container>& x, const stack<T, Container>& y);
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Returns: x.c <=> y.c.

22.6.6.5 Specialized algorithms [stack.special]

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template<class T, class Container> void swap(stack<T, Container>& x, stack<T, Container>& y) noexcept(noexcept(x.swap(y)));
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Constraints: is_­swappable_­v<Container> is true.
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Effects: As if by x.swap(y).