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std::set<Key,Compare,Allocator>:: empty

From cppreference.net

C++
Containers library
std::set
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
bool empty ( ) const ;
(noexcept since C++11)
(constexpr since C++26)

Checks if the container has no elements.

Contents

Return value

true if the container is empty, false otherwise.

Complexity

Constant.

Example

The following code uses empty to check if a std:: set < int > contains any elements:

Run this code 
#include <iostream>
#include <set>
int main()
{
    std::set<int> numbers;
    std::cout << std::boolalpha;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
    numbers.insert(42);
    numbers.insert(19937);
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output: 

Initially, numbers.empty(): true
After adding elements, numbers.empty(): false

See also

returns the number of elements
(public member function)
(C++17)
checks whether the container is empty
(function template)