.capacity()

In C++, the .capacity() method returns the currently allocated storage space for a vector. It differs from the .size() method, which represents the current number of elements in a vector. The value of .capacity() can be equal to or greater than the value of .size(). It indicates the total number of elements that a vector can hold without requiring reallocation. This value is automatically assigned to a vector during initialization.

Syntax

The .capacity() method requires no parameters and can be used as:

myvector.capacity()

• myvector: The vector on which the method is to be applied.

Example

The following example initializes two vectors and returns their capacities using the .capacity() method:

// Comparing vectors with different capacities
#include <iostream>
#include <vector>

int main()
{
  // Initialize two vectors
  std::vector<int> vector_1 = {1, 2, 3};
  std::vector<int> vector_2;

  // Add elements to vector_2
  for (int i = 0; i < 6; i++)
    vector_2.push_back(i);

  // Print the capacity of each vector
  std::cout << "Capacity of vector_1: " <<  vector_1.capacity() << '\n';
  std::cout << "Capacity of vector_2: " <<  vector_2.capacity() << '\n';

  return 0;
}

The above code results in the following output:

Capacity of vector_1: 3
Capacity of vector_2: 8