Skip to content
Related Articles

Related Articles

Improve Article

deque::begin() and deque::end in C++ STL

  • Difficulty Level : Basic
  • Last Updated : 21 Nov, 2018

Deque or Double ended queues are sequence containers with the feature of expansion and contraction on both the ends. They are similar to vectors, but are more efficient in case of insertion and deletion of elements at the end, and also the beginning. Unlike vectors, contiguous storage allocation may not be guaranteed.

deque::begin()

begin() function is used to return an iterator pointing to the first element of the deque container. begin() function returns a bidirectional iterator to the first element of the container.

Want to learn from the best curated videos and practice problems, check out the C++ Foundation Course for Basic to Advanced C++ and C++ STL Course for foundation plus STL.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

Syntax :

dequename.begin()
Parameters :
No parameters are passed.
Returns :
This function returns a bidirectional
iterator pointing to the first element.

Examples:



Input  : mydeque{1, 2, 3, 4, 5};
         mydeque.begin();
Output : returns an iterator to the element 1

Input  : mydeque{8, 7};
         mydeque.begin();
Output : returns an iterator to the element 8

Errors and Exceptions

1. It has a no exception throw guarantee.
2. Shows error when a parameter is passed.




// CPP program to illustrate
// Implementation of begin() function
#include <deque>
#include <iostream>
using namespace std;
  
int main()
{
    // declaration of deque container
    deque<int> mydeque{ 1, 2, 3, 4, 5 };
  
    // using begin() to print deque
    for (auto it = mydeque.begin(); it != mydeque.end(); ++it)
        cout << ' ' << *it;
    return 0;
}

Output:

1 2 3 4 5

Time Complexity : O(1)

deque::end()

end() function is used to return an iterator pointing to the last element of the deque container. end() function returns a bidirectional iterator to the last element of the container.
Note : The last element of any container is considered as the theoretical element next to the last value stored in the container.

Syntax :

dequename.end()
Parameters :
No parameters are passed.
Returns :
This function returns a bidirectional
iterator pointing to the last element.

Examples:

Input  : mydeque{1, 2, 3, 4, 5};
         mydeque.end();
Output : returns an iterator to the element next to the element 5

Input  : mydeque{8, 7};
         mydeque.end();
Output : returns an iterator to the element next to the element 7

Errors and Exceptions

1. It has a no exception throw guarantee.
2. Shows error when a parameter is passed.




// CPP program to illustrate
// Implementation of end() function
#include <deque>
#include <iostream>
using namespace std;
  
int main()
{
    // declaration of deque container
    deque<int> mydeque{ 1, 2, 3, 4, 5 };
  
    // using end() to print deque
    for (auto it = mydeque.begin(); it != mydeque.end(); ++it)
        cout << ' ' << *it;
    return 0;
}

Output:

1 2 3 4 5

Time Complexity : O(1)




My Personal Notes arrow_drop_up
Recommended Articles
Page :