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Showing content from https://www.tutorialspoint.com/cpp_standard_library/cpp_deque_pop_back.htm below:

C++ Deque Pop Back

The C++ std::deque::pop_back() function ia used to remove the last element from the deque container. It reduce the size of the deque by one and invalidates references, pointers, or iterators to the popped element.

When we try to invoke pop_back() function on the empty deque, it results in the undefined behaviour.

Following is the syntax for std::deque::pop_back() function.

void pop_back();

It does not accept any parameters

This function does not return anything.

Calling this function on empty deque causes undefined behavior.

The time complexity of this function is constant i.e. O(1)

In the following example, we are going to consider the basic usage of the pop_back() function.

#include <iostream>
#include <deque>
int main()
{
    std::deque<char> a = {'A', 'B', 'C', 'D'};
    a.pop_back();
    std::cout << "Deque after pop_back(): ";
    for (auto x = a.begin(); x != a.end(); ++x) {
        std::cout << *x << " ";
    }
    std::cout << std::endl;
    return 0;
}

Following is the output of the above code −

Deque after pop_back(): A B C 

Consider the following example, where we are going to handle the empty deque.

#include <iostream>
#include <deque>
int main()
{
    std::deque<int> a;
    if (!a.empty()) {
        a.pop_back();
    } else {
        std::cout << "Deque is empty." << std::endl;
    }
    return 0;
}

Output of the above code is as follows −

Deque is empty.

Let's look at the following example, where we are going to remove the multiple elements from the deque.

#include <iostream>
#include <deque>
int main()
{
    std::deque<char> a = {'A', 'B', 'C', 'D'};
    a.pop_back();
    a.pop_back();
    std::cout << "Deque after pop_back(): ";
    for (auto x = a.begin(); x != a.end(); ++x) {
        std::cout << *x << " ";
    }
    std::cout << std::endl;
    return 0;
}

If we run the above code it will generate the following output −

Deque after pop_back(): A B 

deque.htm

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