C++ flat_set::size() Function

The std::flat_set::size() function in C++, is used to determine the number of elements in a flat_set. It returns the total count of elements stored in the container.

It is used for checking the container current size, helping in capacity management and iteration limits. This function operates in constant time, making it efficient for frequent queries.

Syntax

Following is the syntax for std::flat_set::size() function.

size() const noexcept;

Parameters

It does not accepts any parameter.

Return Value

This function returns the number of elements in the container adaptor.

Example 1

Let's look at the following example, where we are going to consider the basic usage of the size() function.

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > a = {12,23,34};
   std::cout << "Result : " << a.size() << std::endl;
   return 0;
}

Output

Output of the above code is as follows −

Result : 3

Example 2

Consider the following example, where we are going to check the size of the flat_set after erasing the elements using the erase().

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > x = {1,23,43,2};
   std::cout << "Size Before Erasing: " << x.size() << std::endl;
   x.erase(1);
   x.erase(43);
   std::cout << "Size After Erasing: " << x.size() << std::endl;
   return 0;
}

Output

Output of the above code is as follows −

Size Before Erasing: 4
Size After Erasing: 2

Example 3

In the following example, We are going to check the size of the flat_set before and after the insertion of elements.

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > x;
   std::cout << "Size Before Insertion: " << x.size() << std::endl;
   x.insert(12);
   x.insert(23);
   x.insert(34);
   std::cout << "Size After Insertion: " << x.size() << std::endl;
   return 0;
}

Output

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

Size Before Insertion: 0
Size After Insertion: 3