Namespaces
Variants

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

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)
size_type size ( ) const ;
(noexcept since C++11)
(constexpr since C++26)

Returns the number of elements in the container.

Contents

Return value

std:: distance ( begin ( ) , end ( ) )

Complexity

Constant.

Example

Run this code 
#include <cassert>
#include <set>
int main()
{
    std::set<int> nums{4, 2, 4, 2};
    assert(nums.size() == 2);
}

See also

checks whether the container is empty
(public member function)
returns the maximum possible number of elements
(public member function)
(C++17) (C++20)
returns the size of a container or array
(function template)