cppreference.com > C++ Double-ended Queues assign Syntax:
      #include <deque>
      void assign( size_type num, const TYPE& val );
      void assign( input_iterator start, input_iterator end );
The assign() function either gives the current dequeue the values from start to end, or gives it num copies of val. This function will destroy the previous contents of the dequeue. For example, the following code uses assign() to put 10 copies of the integer 42 into a vector:
     vector<int> v;
     v.assign( 10, 42 );
     for( int i = 0; i < v.size(); i++ ) {
       cout << v[i] << " ";
     }
     cout << endl;
The above code displays the following output:
     42 42 42 42 42 42 42 42 42 42
The next example shows how assign() can be used to copy one vector to another:
     vector<int> v1;
     for( int i = 0; i < 10; i++ ) {
       v1.push_back( i );
     }

     vector<int> v2;
     v2.assign( v1.begin(), v1.end() );

     for( int i = 0; i < v2.size(); i++ ) {
       cout << v2[i] << " ";
     }
     cout << endl;
When run, the above code displays the following output:
     0 1 2 3 4 5 6 7 8 9
Related topics: (C++ Strings) assign insert push_back push_front

back
Syntax:

      #include <deque>
      TYPE& back();
      const TYPE& back() const;

The back() function returns a reference to the last element in the dequeue.

For example:

     vector<int> v;
     for( int i = 0; i < 5; i++ ) {
       v.push_back(i);
     }
     cout << "The first element is " << v.front()
          << " and the last element is " << v.back() << endl;

This code produces the following output:

     The first element is 0 and the last element is 4

The back() function runs in constant time.

Related topics:
front
pop_back

at
Syntax:

      #include <deque>
      TYPE& at( size_type loc );
      const TYPE& at( size_type loc ) const;

The at() function returns a reference to the element in the dequeue at index loc. The at() function is safer than the [] operator, because it won't let you reference items outside the bounds of the dequeue.

For example, consider the following code:

     vector<int> v( 5, 1 );
     for( int i = 0; i < 10; i++ ) {
       cout << "Element " << i << " is " << v[i] << endl;
     }

This code overrunns the end of the vector, producing potentially dangerous results. The following code would be much safer:

     vector<int> v( 5, 1 );
     for( int i = 0; i < 10; i++ ) {
       cout << "Element " << i << " is " << v.at(i) << endl;
     }

Instead of attempting to read garbage values from memory, the at() function will realize that it is about to overrun the vector and will throw an exception.

Related topics:
(C++ Multimaps) Container operators
Container operators

max_size
Syntax:

      #include <deque>
      size_type max_size() const;

The max_size() function returns the maximum number of elements that the dequeue can hold. The max_size() function should not be confused with the size() or (C++ Strings) capacity() functions, which return the number of elements currently in the dequeue and the the number of elements that the dequeue will be able to hold before more memory will have to be allocated, respectively.

Related topics:
size

begin
Syntax:

      #include <deque>
      iterator begin();
      const_iterator begin() const;

The function begin() returns an iterator to the first element of the dequeue. begin() should run in constant time.

For example, the following code uses begin() to initialize an iterator that is used to traverse a list:

       // Create a list of characters
       list<char> charList;
       for( int i=0; i < 10; i++ ) {
         charList.push_front( i + 65 );
       }
       // Display the list
       list<char>::iterator theIterator;
       for( theIterator = charList.begin(); theIterator != charList.end(); theIterator++ ) {
         cout << *theIterator;
       }

Related topics:
end
rbegin
rend

clear
Syntax:

      #include <deque>
      void clear();

The function clear() deletes all of the elements in the dequeue. clear() runs in linear time.

Related topics:
erase

Container [] operator
Syntax:

      TYPE& operator[]( size_type index );  const TYPE& operator[]( size_type index ) const;

Individual elements of a dequeue can be examined with the [] operator.

For example, the following code uses the [] operator to access all of the elements of a vector:

     vector<int> v( 5, 1 );
     for( int i = 0; i < v.size(); i++ ) {
       cout << "Element " << i << " is " << v[i] << endl;
     }

The [] operator runs in constant time.

Related topics:
at

Container [] operator
Syntax:

      TYPE& operator[]( size_type index );  const TYPE& operator[]( size_type index ) const;

Individual elements of a dequeue can be examined with the [] operator.

For example, the following code uses the [] operator to access all of the elements of a vector:

     vector<int> v( 5, 1 );
     for( int i = 0; i < v.size(); i++ ) {
       cout << "Element " << i << " is " << v[i] << endl;
     }

The [] operator runs in constant time.

Related topics:
at

empty
Syntax:

      #include <deque>
      bool empty() const;

The empty() function returns true if the dequeue has no elements, false otherwise.

For example, the following code uses empty() as the stopping condition on a (C/C++ Keywords) while loop to clear a dequeue and display its contents in reverse order:

     vector<int> v;
     for( int i = 0; i < 5; i++ ) {
       v.push_back(i);
     }
     while( !v.empty() ) {
       cout << v.back() << endl;
       v.pop_back();
     }

Related topics:
size

end
Syntax:

      #include <deque>
      iterator end();
      const_iterator end() const;

The end() function returns an iterator just past the end of the dequeue.

Note that before you can access the last element of the dequeue using an iterator that you get from a call to end(), you'll have to decrement the iterator first.

For example, the following code uses begin() and end() to iterate through all of the members of a vector:

     vector<int> v1( 5, 789 );
     vector<int>::iterator it;
     for( it = v1.begin(); it != v1.end(); it++ ) {
       cout << *it << endl;
     }

The iterator is initialized with a call to begin(). After the body of the loop has been executed, the iterator is incremented and tested to see if it is equal to the result of calling end(). Since end() returns an iterator pointing to an element just after the last element of the vector, the loop will only stop once all of the elements of the vector have been displayed.

end() runs in constant time.

Related topics:
begin
rbegin
rend

Container constructors & destructors
Syntax:

      container();  container( const container& c );  ~container();

Every dequeue has a default constructor, copy constructor, and destructor.

The default constructor takes no arguments, creates a new instance of that dequeue, and runs in constant time. The default copy constructor runs in linear time and can be used to create a new dequeue that is a copy of the given dequeue c.

The default destructor is called when the dequeue should be destroyed.

For example, the following code creates a pointer to a vector of integers and then uses the default dequeue constructor to allocate a memory for a new vector:

     vector<int>* v;
     v = new vector<int>();

Related topics:
Special container constructors, resize

Container constructors
Syntax:

      #include <deque>
      container();
      container( const container& c );
      container( size_type num, const TYPE& val = TYPE() );
      container( input_iterator start, input_iterator end );
      ~container();

The default dequeue constructor takes no arguments, creates a new instance of that dequeue.

The second constructor is a default copy constructor that can be used to create a new dequeue that is a copy of the given dequeue c.

The third constructor creates a dequeue with space for num objects. If val is specified, each of those objects will be given that value. For example, the following code creates a vector consisting of five copies of the integer 42:

     vector<int> v1( 5, 42 );

The last constructor creates a dequeue that is initialized to contain the elements between start and end. For example:

     // create a vector of random integers
     cout << "original vector: ";
     vector<int> v;
     for( int i = 0; i < 10; i++ ) {
       int num = (int) rand() % 10;
       cout << num << " ";
       v.push_back( num );
     }
     cout << endl;

     // find the first element of v that is even
     vector<int>::iterator iter1 = v.begin();
     while( iter1 != v.end() && *iter1 % 2 != 0 ) {
       iter1++;
     }

     // find the last element of v that is even
     vector<int>::iterator iter2 = v.end();
     do {
       iter2--;
     } while( iter2 != v.begin() && *iter2 % 2 != 0 );

     cout << "first even number: " << *iter1 << ", last even number: " << *iter2 << endl;

     cout << "new vector: ";
     vector<int> v2( iter1, iter2 );
     for( int i = 0; i < v2.size(); i++ ) {
       cout << v2[i] << " ";
     }
     cout << endl;

When run, this code displays the following output:

     original vector: 1 9 7 9 2 7 2 1 9 8
     first even number: 2, last even number: 8
     new vector: 2 7 2 1 9

All of these constructors run in linear time except the first, which runs in constant time.

The default destructor is called when the dequeue should be destroyed.

Container operators
Syntax:

      #include <deque>
      TYPE& operator[]( size_type index );
      const TYPE& operator[]( size_type index ) const;
      container operator=(const container& c2);
      bool operator==(const container& c1, const container& c2);
      bool operator!=(const container& c1, const container& c2);
      bool operator<(const container& c1, const container& c2);
      bool operator>(const container& c1, const container& c2);
      bool operator<=(const container& c1, const container& c2);
      bool operator>=(const container& c1, const container& c2);

All of the C++ containers can be compared and assigned with the standard comparison operators: ==, !=, <=, >=, <, >, and =. Individual elements of a dequeue can be examined with the [] operator.

Performing a comparison or assigning one dequeue to another takes linear time. The [] operator runs in constant time.

Two `containers` are equal if:

1. Their size is the same, and
2. Each member in location i in one dequeue is equal to the the member in location i in the other dequeue.

Comparisons among dequeues are done lexicographically.

For example, the following code uses the [] operator to access all of the elements of a vector:

     vector<int> v( 5, 1 );
     for( int i = 0; i < v.size(); i++ ) {
       cout << "Element " << i << " is " << v[i] << endl;
     }

Related topics:
at

erase
Syntax:

      #include <deque>
      iterator erase( iterator loc );
      iterator erase( iterator start, iterator end );

The erase() function either deletes the element at location loc, or deletes the elements between start and end (including start but not including end). The return value is the element after the last element erased.

The first version of erase (the version that deletes a single element at location loc) runs in constant time for lists and linear time for vectors, dequeues, and strings. The multiple-element version of erase always takes linear time.

For example:

     // Create a vector, load it with the first ten characters of the alphabet
     vector<char> alphaVector;
     for( int i=0; i < 10; i++ ) {
       alphaVector.push_back( i + 65 );
     }
     int size = alphaVector.size();
     vector<char>::iterator startIterator;
     vector<char>::iterator tempIterator;
     for( int i=0; i < size; i++ ) {
       startIterator = alphaVector.begin();
       alphaVector.erase( startIterator );
       // Display the vector
       for( tempIterator = alphaVector.begin(); tempIterator != alphaVector.end(); tempIterator++ ) {
         cout << *tempIterator;
       }
       cout << endl;
     }

That code would display the following output:

     BCDEFGHIJ
     CDEFGHIJ
     DEFGHIJ
     EFGHIJ
     FGHIJ
     GHIJ
     HIJ
     IJ
     J

In the next example, erase() is called with two iterators to delete a range of elements from a vector:

     // create a vector, load it with the first ten characters of the alphabet
     vector<char> alphaVector;
     for( int i=0; i < 10; i++ ) {
       alphaVector.push_back( i + 65 );
     }
     // display the complete vector
     for( int i = 0; i < alphaVector.size(); i++ ) {
       cout << alphaVector[i];
     }
     cout << endl;

     // use erase to remove all but the first two and last three elements
     // of the vector
     alphaVector.erase( alphaVector.begin()+2, alphaVector.end()-3 );
     // display the modified vector
     for( int i = 0; i < alphaVector.size(); i++ ) {
       cout << alphaVector[i];
     }
     cout << endl;

When run, the above code displays:

     ABCDEFGHIJ
     ABHIJ

Related topics:
clear
insert
pop_back
pop_front
(C++ Lists) remove
(C++ Lists) remove_if

front
Syntax:

      #include <deque>
      TYPE& front();
      const TYPE& front() const;

The front() function returns a reference to the first element of the dequeue, and runs in constant time.

Related topics:
back
pop_front
push_front

insert
Syntax:

      #include <deque>
      iterator insert( iterator loc, const TYPE& val );
      void insert( iterator loc, size_type num, const TYPE& val );
      template<TYPE> void insert( iterator loc, input_iterator start, input_iterator end );

The insert() function either:

- inserts val before loc, returning an iterator to the element inserted,
- inserts num copies of val before loc, or
- inserts the elements from start to end before loc.

For example:

     // Create a vector, load it with the first 10 characters of the alphabet
     vector<char> alphaVector;
     for( int i=0; i < 10; i++ ) {
       alphaVector.push_back( i + 65 );
     }

     // Insert four C's into the vector
     vector<char>::iterator theIterator = alphaVector.begin();
     alphaVector.insert( theIterator, 4, 'C' );

     // Display the vector
     for( theIterator = alphaVector.begin(); theIterator != alphaVector.end(); theIterator++ )    {
       cout << *theIterator;
     }

This code would display:

     CCCCABCDEFGHIJ

Related topics:
assign
erase
(C++ Lists) merge
push_back
push_front
(C++ Lists) splice

pop_back
Syntax:

      #include <deque>
      void pop_back();

The pop_back() function removes the last element of the dequeue.

pop_back() runs in constant time.

Related topics:
back
erase
pop_front
push_back

pop_front
Syntax:

      #include <deque>
      void pop_front();

The function pop_front() removes the first element of the dequeue.

The pop_front() function runs in constant time.

Related topics:
erase
front
pop_back
push_front

push_back
Syntax:

      #include <deque>
      void push_back( const TYPE& val );

The push_back() function appends val to the end of the dequeue.

For example, the following code puts 10 integers into a list:

       list<int> the_list;
       for( int i = 0; i < 10; i++ )
         the_list.push_back( i );

When displayed, the resulting list would look like this:

     0 1 2 3 4 5 6 7 8 9

push_back() runs in constant time.

Related topics:
assign
insert
pop_back
push_front

push_front
Syntax:

      #include <deque>
      void push_front( const TYPE& val );

The push_front() function inserts val at the beginning of dequeue.

push_front() runs in constant time.

Related topics:
assign
front
insert
pop_front
push_back

rbegin
Syntax:

      #include <deque>
      reverse_iterator rbegin();
      const_reverse_iterator rbegin() const;

The rbegin() function returns a reverse_iterator to the end of the current dequeue.

rbegin() runs in constant time.

Related topics:
begin
end
rend

rend
Syntax:

      #include <deque>
      reverse_iterator rend();
      const_reverse_iterator rend() const;

The function rend() returns a reverse_iterator to the beginning of the current dequeue.

rend() runs in constant time.

Related topics:
begin
end
rbegin

resize
Syntax:

      #include <deque>
      void resize( size_type num, const TYPE& val = TYPE() );

The function resize() changes the size of the dequeue to size. If val is specified then any newly-created elements will be initialized to have a value of val.

This function runs in linear time.

Related topics:
(C++ Multimaps) Container constructors & destructors
(C++ Strings) capacity
size

size
Syntax:

      #include <deque>
      size_type size() const;

The size() function returns the number of elements in the current dequeue.

Related topics:
(C++ Strings) capacity
empty
(C++ Strings) length
max_size
resize

swap
Syntax:

      #include <deque>
      void swap( const container& from );

The swap() function exchanges the elements of the current dequeue with those of from. This function operates in constant time.

For example, the following code uses the swap() function to exchange the values of two strings:

       string first( "This comes first" );
       string second( "And this is second" );
       first.swap( second );
       cout << first << endl;
       cout << second << endl;

The above code displays:

       And this is second
       This comes first

Related topics:
(C++ Lists) splice