cppreference.com > C++ Double-ended Queues > begin 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