#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.