C++ size()

The size() function returns the number of elements currently stored in a std::deque container. It has constant time complexity (O(1)) and is marked noexcept since C++ 11.

Syntax

deque_object.size();

Parameters:

This function does not take any parameters.

Return value:

Returns a value of type size_type (an unsigned integral type) representing the number of elements in the deque.

Example 1

In this example, the size method is used to check the element count of an initially empty deque, then after push_back operations:

#include <deque>
#include <iostream>

int main() {
  std::deque<int> d;
  std::cout << "Initial size: " << d.size() << "\n";

  for (int i = 0; i < 5; ++i) {
    d.push_back(i);
  }
  std::cout << "Size after push_back 5 elements: " << d.size() << "\n";

  return 0;
}

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The output of this code is:

Initial size: 0
Size after push_back 5 elements: 5

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Example 2

In this example, the size method is used after insert and pop operations to illustrate dynamic changes in element count:

#include <deque>
#include <iostream>

int main() {
  std::deque<int> d = {1, 2, 3};
  std::cout << "Initial size: " << d.size() << "\n";

  d.pop_front();
  d.pop_back();
  std::cout << "Size after two pops: " << d.size() << "\n";

  d.insert(d.begin(), 10);
  std::cout << "Size after one insert at front: " << d.size() << "\n";

  return 0;
}

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The output of this code is:

Initial size: 3
Size after two pops: 1
Size after one insert at front: 2

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Codebyte Example

In this example, the size() method is repeatedly checked in a loop until the deque becomes empty:

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Frequently Asked Questions

1. What does size() do in C++?

The size() function in C++ returns the number of elements present in a container, such as a std::deque, std::vector, or std::string. It gives the current length of the container in constant time (O(1)) without modifying it.

2. What is a deque function in C++?

A deque (double-ended queue) in C++ is a Standard Template Library (STL) container that allows insertion and deletion of elements from both the front and back efficiently.

3. How to get the size of a deque in C++?

You can get the number of elements in a deque using the size() member function.