## deque

    Container

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Interface
- Constructors
- Destructors
- Allocators
- Iterators
- Assignment Operators
- Reference Operators
- Member Functions
- Non-member Functions
- Specialized Algorithms
- Example
- Warnings

### Summary

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

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

Data Types
allocator

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

### Synopsis

    #include <deque>

    template <class T, class Allocator = allocator<T> >
     class deque;

### Description

deque<T, Allocator> 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 (where `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

    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
               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);
       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();
    };

     // Non-member 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>
     voice 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 list 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 list 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 first, InputIterator last,
           const Allocator& alloc = Allocator());

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

### Destructors

    ~deque();

Releases any allocated memory for self.

### Allocators

    allocator
    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 first, InputIterator last);

Erases all elements contained in self, then inserts new elements from the range `[first, last)`.

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

Erases all elements contained in self, then inserts `n` instances of the value of `t.`

    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 first, iterator last);

Deletes the elements in the range (`first, last`). 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 T& x);

Inserts `x` before `position`. The return value points to the inserted `x`.

    void
    insert(iterator position, size_type n, const T& x);

Inserts `n` copies of `x` before `position`.

    template <class InputIterator>
    void
    insert(iterator position, InputIterator first,
            InputIterator last);

Inserts copies of the elements in the range `(first, last]` before `position`.

    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);

Alters the size of self. If the new size (`sz`) is greater than the current size, then `sz-size()` copies of the default value of type `T` 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. Type `T` must have a default constructor.

    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`.

### Non-member 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 <string>
     #include <iostream>
     using namespace std;

     deque<string, allocator> deck_of_cards;
     deque<string, allocator> current_hand;

     void initialize_cards(deque<string, allocator>& cards) {
       cards.push_front("aceofspades");
       cards.push_front("kingofspades");
       cards.push_front("queenofspades");
       cards.push_front("jackofspades");
       cards.push_front("tenofspades");
       // etc.
     }

     template <class It, class It2>
     void print_current_hand(It start, It2 end)
     {
       while (start < end)
       cout << *start++ << 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

    aceofspades
    kingofspades
    queenofspades
    jackofspades
    tenofspades

### Warnings

Member function templates are used in all containers in by the Standard Template Library. An example of this is the constructor for deque<T, Allocator>, which 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());

But not this way:

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

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

Additionally, many compilers do not support default template arguments. If your compiler is one of these, you always need to supply the `Allocator` template argument. For instance, you have to write:

`deque<int, allocator<int> >`

instead of:

`deque<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998