C++ flat_set::empty() Function

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The std::flat_set::empty() function in C++, is used to check whether the flat_set is empty. A flat_set is a ordered container that stores the unique elements in a sorted sequence. This function returns true if the set contains no elements, otherwise it returns false.

This function operates in constant time O(1) and is useful for validating if a flat_set needs further operations like insertion or iteration.

Syntax

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

bool empty() const noexcept;

Parameters

It does not accepts any parameter.

Return Value

This function returns true if the container is empty otherwise false.

Example 1

Let's look at the following example, where we are going to check whether the flat_set is empty or not.

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > x;
   if (x.empty()) {
      std::cout << "It is Empty.\n";
   } else {
      std::cout << "It Is Not Empty.\n";
   }
   return 0;
}

Output

Output of the above code is as follows −

It is Empty.

Example 2

Consider the following example, where we are going to initialize the flat_set with elements and apply the clear() to remove the elements and apply the empty() function.

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > a = {11,12,23};
   a.clear();
   if (a.empty()) {
      std::cout << "It Is Empty After Clearing.\n";
   } else {
      std::cout << "It Is Not Empty.\n";
   }
   return 0;
}

Output

Output of the above code is as follows −

It Is Empty After Clearing.

Example 3

In the following example, We are going to insert the elements in the flat_set, then applying the empty() and observing the output.

#include <iostream>
#include <boost/container/flat_set.hpp>
int main() {
   boost::container::flat_set < int > a;
   std::cout << "Initially, is falt_set empty? " << (a.empty() ? "Yes\n" : "No\n");
   a.insert(112);
   std::cout << "After insertion, is flat_set empty? " << (a.empty() ? "Yes\n" : "No\n");
   return 0;
}

Output

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

Initially, is falt_set empty? Yes
After insertion, is flat_set empty? No