Apache C++ Standard Library Reference Guide

## deque

Library: Containers

    Does not inherit

- Local Index
- Summary
- Synopsis
- Description
- Interface
- Constructors
- Destructors
- Allocators
- Iterators
- Assignment Operators
- Reference Operators
- Member Functions
- Nonmember Functions
- Specialized Algorithms
- Example
- Warnings
- Standards Conformance

### Local Index

#### Members

assign() at() back() begin() clear() deque() empty() | end() erase() front() get_allocator() insert() max_size() operator=() | operator[]() pop_back() pop_front() push_back() push_front() rbegin() rend() | resize() size() swap() ~deque()

#### Non-Members

operator!=() operator>() | operator>=() operator<() | operator<=() operator==() |

### Summary

A sequence that supports random access iterators and efficient insertion/deletion at both beginning and end

### Synopsis

    #include <deque>

    namespace std {
      template <class T, class Allocator = allocator<T> >
      class deque;
    }

### Description

deque is a type of sequence that supports random access iterators. It supports constant time insert and erase operations at the beginning or the end of the container. Insertion and erase in the middle take linear time. Storage management is handled by the `Allocator` template parameter.

Any type used for the template parameter `T` must include the following members. Here `T` is the `type`, `t` is a `value` of `T`, and `u` is a `const` `value` of `T`:

`Copy constructors` | `T(t)` and `T(u)`
`Destructor` | `t.~T()`
`Address of` | `&t` and `&u` yielding `T*` and `const T*` respectively
`Assignment` | `t = a` where `a` is a (possibly `const`) value of `T`

### Interface

    namespace std {
      template <class T, class Allocator = allocator<T> >
      class deque {

      public:

        // Types

        class iterator;
        class const_iterator;

        typedef T value_type;
        typedef Allocator allocator_type;
        typedef typename Allocator::reference reference;
        typedef typename Allocator::const_reference const_reference;
        typedef typename Allocator::size_type size_type;
        typedef typename Allocator::difference_type difference_type;
        typedef typename Allocator::pointer pointer;
        typedef typename Allocator::const_pointer
          const_pointer;
        typedef typename std::reverse_iterator<iterator>
          reverse_iterator;
        typedef typename std::reverse_iterator<const_iterator>
          const_reverse_iterator;

        // Construct/Copy/Destroy

        explicit deque(const Allocator& = Allocator());
        explicit deque(size_type);
        deque(size_type, const T& value,
               const Allocator& = Allocator ());
        deque(const deque<T,Allocator>&);
        template <class InputIterator>
        deque(InputIterator, InputIterator,
              const Allocator& = Allocator ());
        ~deque ();
        deque<T,Allocator>& operator=(const deque<T,Allocator>&);
        template <class InputIterator>
        void assign (InputIterator, InputIterator);
        void assign (size_type, const T&);
        allocator_type get allocator () const;

        // Iterators

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

        // Capacity

        size_type size() const;
        size_type max_size() const;
        void resize(size_type, T);
        bool empty() const;

       // Element access

       reference operator[](size_type);
       const_reference operator[](size_type) const;
       reference at(size_type);
       const_reference at(size_type) const;
       reference front();
       const_reference front() const;
       reference back();
       const_reference back() const;

       // Modifiers

         void push_front(const T&);
         void push_back(const T&);
         iterator insert(iterator, const T&);
         void insert(iterator, size_type, const T&);
         template <class InputIterator>
         void insert(iterator, InputIterator, InputIterator);

         void pop_front();
         void pop_back();

         iterator erase(iterator);
         iterator erase(iterator, iterator);
         void swap(deque<T, Allocator>&);
         void clear();
      };

      // Nonmember Operators

      template <class T, class Allocator>
      bool operator==(const deque<T, Allocator>&,
                      const deque<T, Allocator>&);

      template <class T, class Allocator>
      bool operator!=(const deque<T, Allocator>&,
                      const deque<T, Allocator>&);

      template <class T, class Allocator>
      bool operator<(const deque<T, Allocator>&,
                     const deque<T, Allocator>&);

      template <class T, class Allocator>
      bool operator>(const deque<T, Allocator>&,
                     const deque<T, Allocator>&);

      template <class T, class Allocator>
      bool operator<=(const deque<T, Allocator>&,
                      const deque<T, Allocator>&);

      template <class T, class Allocator>
      bool operator>=(const deque<T, Allocator>&,
                      const deque<T, Allocator>&);

      // Specialized Algorithms

      template <class T, class Allocator>
      void swap(deque<T, Allocator>&, deque<T, Allocator>&);
    }

### Constructors

    explicit
    deque(const Allocator& alloc = Allocator());

The default constructor. Creates a deque of zero elements. The deque uses the allocator `alloc` for all storage management.

    explicit
    deque(size_type n);

Creates a deque of length `n`, containing `n` copies of the default value for type `T`. `T` must have a default constructor. The deque uses the allocator `Allocator()` for all storage management.

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

Creates a deque of length `n`, containing `n` copies of `value`. The deque uses the allocator `alloc` for all storage management.

    deque(const deque<T, Allocator>& x);

Creates a copy of `x`.

    template <class InputIterator>
    deque(InputIterator start, InputIterator finish,
           const Allocator& alloc = Allocator());

Creates a deque of length `finish - start`, filled with all values obtained by dereferencing the `InputIterators` on the range `[start, finish)`. The deque uses the allocator `alloc` for all storage management.

### Destructors

    ~deque();

Releases any allocated memory for self.

### Allocators

    allocator_type get_allocator() const;

Returns a copy of the allocator used by self for storage management.

### Iterators

    iterator begin();

Returns a random access iterator that points to the first element.

    const_iterator begin() const;

Returns a constant random access iterator that points to the first element.

    iterator end();

Returns a random access iterator that points to the past-the-end value.

    const_iterator end() const;

Returns a constant random access iterator that points to the past-the-end value.

    reverse_iterator rbegin();

Returns a random access `reverse_iterator` that points to the past-the-end value.

    const_reverse_iterator rbegin() const;

Returns a constant random access reverse iterator that points to the past-the-end value.

    reverse_iterator rend();

Returns a random access `reverse_iterator` that points to the first element.

    const_reverse_iterator rend() const;

Returns a constant random access reverse iterator that points to the first element.

### Assignment Operators

    deque<T, Allocator>&
    operator=(const deque<T, Allocator>& x);

Erases all elements in self, then inserts into self a copy of each element in `x`. Returns a reference to self.

### Reference Operators

    reference operator[](size_type n);

Returns a `reference` to element `n` of self. The result can be used as an lvalue. The index `n` must be between `0` and the `size() - 1`..

    const_reference operator[](size_type n) const;

Returns a constant reference to element `n` of self. The index `n` must be between `0` and the `size() - 1`.

### Member Functions

    template <class InputIterator>
    void
    assign(InputIterator start, InputIterator finish);

If InputIterator is an integral type, the function calls `assign(size_type(start), value_type (finish))`. Otherwise, the function replaces elements in `*this` with copies of those in the range `[start, finish)`. The function invalidates all iterators and references to elements in `*this`.

    void
    assign(size_type n, const T& t);

Replaces elements in `*this` with `n` copies of `t`. The function invalidates all iterators and references to elements in `*this`.

    reference
    at(size_type n);

Returns a reference to element `n` of self. The result can be used as an lvalue. The index `n` must be between `0` and the`size() - 1`.

    const_reference
    at(size_type) const;

Returns a constant reference to element `n` of self. The index `n` must be between `0` and the `size() - 1`.

    reference
    back();

Returns a reference to the last element.

    const_reference
    back() const;

Returns a constant reference to the last element.

    void
    clear();

Erases all elements from the self.

    bool
    empty() const;

Returns `true` if the size of self is zero.

    reference
    front();

Returns a reference to the first element.

    const_reference
    front() const;

Returns a constant reference to the first element.

    iterator
    erase(iterator start, iterator finish);

Deletes the elements in the range `[start, finish)`. Returns an iterator pointing to the element following the last deleted element, or `end()` if there were no elements after the deleted range.

    iterator
    erase(iterator position);

Removes the element pointed to by `position`. Returns an iterator pointing to the element following the deleted element, or `end()` if there were no elements after the deleted range.

    iterator
    insert(iterator position, const_reference x);

Requires that `position` be a valid iterator into `*this`. Inserts a copy of `x` into `*this` at `position`. Returns an iterator pointing to the inserted copy of `x`. The function invalidates all iterators into `*this`.

Unless `(position == begin() || position == end())` holds, the function invalidates all references to elements in `*this`.

    void
    insert(iterator position, size_type n, const_reference x);

Requires that `position` be a valid iterator into `*this`. Inserts `n` copies of `x` into `*this` at `position`. The function invalidates all iterators into `*this`.

Unless `(position == begin() || position == end())` holds, the function invalidates all references to elements in `*this`.

    template <class InputIterator>
    void
    insert(iterator position, InputIterator start, InputIterator finish);

Requires that `position` be a valid iterator into `*this`. If InputIterator is an integral type, the function calls `insert(position, size_type(start), value_type (finish))`. Otherwise the function inserts copies of elements in the range `[start, finish)` at `position`. The function invalidates all iterators into `*this`.

Unless `(position == begin() || position == end())` holds, the function invalidates all references to elements in `*this`.

    size_type
    max_size() const;

Returns `size()` of the largest possible deque.

    void
    pop_back();

Removes the last element. Note that this function does not return the element.

    void
    pop_front();

Removes the first element. Note that this function does not return the element.

    void
    push_back(const T& x);

Appends a copy of `x` to the end.

    void
    push_front(const T& x);

Inserts a copy of `x` at the front.

    void
    resize(size_type sz, T c);

Alters the size of self. If the new size (`sz`) is greater than the current size, then `sz-size()` `c`'s are inserted at the end of the deque. If the new size is smaller than the current capacity, then the deque is truncated by erasing `size()-sz` elements off the end. Otherwise, no action is taken.

    size_type
    size() const;

Returns the number of elements.

    void
    swap(deque<T,Allocator>& x);

Exchanges self with `x`.

### Nonmember Functions

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

Equality operator. Returns `true` if `x` is the same as `y`.

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

Returns `true` if `x` is not the same as `y`.

    template <class T, class Allocator>
    bool operator<(const deque<T, Allocator>& x,
                    const deque<T, Allocator>& y);

Returns `true` if the elements contained in `x` are lexicographically less than the elements contained in `y`.

    template <class T, class Allocator>
    bool operator>(const deque<T, Allocator>& x,
                    const deque<T, Allocator>& y);

Returns `true` if the elements contained in `x` are lexicographically greater than the elements contained in `y`.

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

Returns `true` if the elements contained in `x` are lexicographically less than or equal to the elements contained in `y`.

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

Returns `true` if the elements contained in `x` are lexicographically greater than or equal to the elements contained in `y`.

    template <class T, class Allocator>
    bool operator<(const deque<T, Allocator>& x,
                    const deque<T, Allocator>& y);

Returns `true` if the elements contained in `x` are lexicographically less than the elements contained in `y`.

### Specialized Algorithms

    template <class T, class Allocator>
    void swap(deque<T, Allocator>& a, deque<T, Allocator>& b);

Swaps the contents of `a` and `b`.

### Example

    //
    // deque.cpp
    //

    #include <deque>
    #include <iostream>
    #include <string>

    typedef std::deque<std::string,
                       std::allocator<std::string> > deque;

    static deque deck_of_cards;
    static deque current_hand;

    void initialize_cards (deque &cards)
    {
        cards.push_front ("ace of spades");
        cards.push_front ("king of spades");
        cards.push_front ("queen of spades");
        cards.push_front ("jack of spades");
        cards.push_front ("ten of spades");
        //
        // etc.
        //
    }

    template <class It, class It2>
    void print_current_hand (It start, It2 end)
    {
        while (start < end)
            std::cout << *start++ << std::endl;
    }

    template <class It, class It2>
    void deal_cards (It, It2 end)
    {
        for (int i = 0; i < 5; i++) {
            current_hand.insert (current_hand.begin (), *end);
            deck_of_cards.erase (end++);
        }
    }

    void play_poker ()
    {
        initialize_cards (deck_of_cards);
        deal_cards (current_hand.begin (),
                    deck_of_cards.begin ());
    }

    int main ()
    {
        play_poker ();

        print_current_hand (current_hand.begin (),
                            current_hand.end ());

        return 0;
    }

    Program Output:

    ace of spades
    king of spades
    queen of spades
    jack of spades
    ten of spades

### Warnings

Member function templates are used in all the containers in the Standard Template Library. For example, the constructor for deque takes two templatized iterators:

     template <class InputIterator>
     deque (InputIterator, InputIterator);

deque also has an insert function of this type. These functions, when not restricted by compiler limitations, allow you to use any type of input iterator as arguments. For compilers that do not support this feature, substitute functions allow you to use an iterator obtained from the same type of container as the one you are constructing (or calling a member function on), or you can use a pointer to the type of element you have in the container.

For example, if your compiler does not support member function templates you can construct a deque in the following two ways:

    int intarray[10];
    deque<int> first_deque(intarray, intarray + 10);
    deque<int> second_deque(first_deque.begin(),
                            first_deque.end());

You cannot construct a deque this way:

    deque<long> long_deque(first_deque.begin(),
                                      first_deque.end());

since the`long_deque` and `first_deque` are not the same type.

### Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++Section 23.2.1