Difference Between deque::cbegin and deque::assign in C++

Deque or Double-ended queues are sequence containers with the feature of expansion and contraction on both ends. They are similar to vectors, but are more efficient in the case of insertion and deletion of elements at the end, and also the beginning. Unlike vectors, contiguous storage allocation may not be guaranteed. Here we will see the difference between deque::assign and deque::at in C++.

deque::cbegin

deque::cbegin is used to return a const iterator pointing to the first element in the container. We cannot use this to modify the contents the iterator points to.

Syntax:

const_iterator cbegin();

Parameters: None

Return Value: A const_iterator to the beginning of the sequence.

Iterator Validity: There is no change in Iterator Validity

Header File:

<deque>

Exceptions: It never throws exceptions

Example:

C++

// C++ program to demonstrate deque::cbegin

#include <deque>
#include <iostream>
using namespace std;

// Driver code
int main()
{
    // Declaration of Deque
    deque<int> GFG = { 1, 2, 3, 4, 5 };

    cout << "Elements in Deque Container are : ";
    for (auto it = GFG.cbegin(); it != GFG.cend(); ++it) {
        cout << *it << " ";
    }
    cout << endl;
    return 0;
}

Output:

Elements in Deque Container are : 1 2 3 4 5 

• Time Complexity – O(1)
• Space Complexity – O(1)

deque::assign

deque::assign is used to assign new contents to the deque container by replacing its current contents. It modifies the size accordingly.

Syntax:

dequename.assign(<int> size, <int> val)

Parameters:

1. size: it specifies the number of values to be assigned to the container.
2. val: it specifies the value to be assigned to the container.

Return Value: None

Iterator Validity: In this container, all the iterators, pointers, and references are invalidated.

Header File:

<deque>

Exceptions: If an exception is thrown, the container is in a valid state.

Example:

C++

// C++ program to demonstrate deque::assign

#include <deque>
#include <iostream>
using namespace std;

// Driver code
int main()
{
    // Declaration of Deque
    deque<int> A = { 10, 20, 30, 40, 50, 60 };
    deque<int> B;

    // Iterator for deque to traverse
    deque<int>::iterator itr = B.begin();

    // Assigning deque A elements
    // into deque B
    B.assign(A.begin(), A.end());

    cout << "Elements in Deque B are : ";
    for (itr = B.begin(); itr != B.end(); ++itr) {
        cout << *itr << " ";
    }

    cout << endl;
    return 0;
}

Output:

Elements in Deque B are : 10 20 30 40 50 60 

• Time Complexity: O(N)
• Space Complexity: O(N)

deque::assign vs deque::cbegin

Below are the differences between deque::assign and deque::cbegin

Basis	deque::cbegin	deque::assign
Definition	It is used to return a const iterator pointing to the first element in the container.	It is used to assign new contents to the deque container, replacing its current contents
Syntax	const_iterator cbegin();	dequename.assign(<int> size, <int> val);
Parameters	It does not take any parameters.	It takes two parameters i.e. size and val
Return Value	Its return value is a const_iterator to the beginning of the sequence.	It does not have any return type.
Complexity	Constant	Linear