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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Iterator invalidation

Member function table

Non-member function table

 

std::set

Member functions

set::set

set::~set

set::operator=

set::get_allocator

Iterators

set::beginset::cbegin (C++11)

set::endset::cend (C++11)

set::rbeginset::crbegin (C++11)

set::rendset::crend (C++11)

Capacity

set::empty

set::size

set::max_size

Modifiers

set::clear

set::insert

set::insert_range (C++23)

set::emplace (C++11)

set::emplace_hint (C++11)

set::erase

set::swap

set::extract (C++17)

set::merge (C++17)

Lookup

set::count

set::find

set::contains (C++20)

set::equal_range

set::lower_bound

set::upper_bound

Observers

set::key_comp

set::value_comp

Non-member functions

std::swap

erase_if (C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Deduction guides(C++17)

 

bool empty() const;		(until C++11)
bool empty() const noexcept;		(since C++11) (until C++20)
[[nodiscard]] bool empty() const noexcept;		(since C++20)

Checks if the container has no elements, i.e. whether begin() == end().

Parameters

(none)

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 <set>
#include <iostream>
 
int main()
{
    std::set<int> numbers;
    std::cout << std::boolalpha;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
 
    numbers.insert(42);
    numbers.insert(13317); 
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output:

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

See also

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