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

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

Returns the number of elements in the container, i.e. std::distance (begin( ), end( ) )

(none)

The number of elements in the container.

Constant.

Run this code

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

Compiler support
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Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
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Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

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