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

 

C++

Compiler support

Freestanding and hosted

Language

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

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

Views

span (C++20)

 

std::multiset

Member functions

multiset::multiset

multiset::~multiset

multiset::operator=

multiset::get_allocator

Iterators

multiset::beginmultiset::cbegin (C++11)

multiset::endmultiset::cend (C++11)

multiset::rbeginmultiset::crbegin (C++11)

multiset::rendmultiset::crend (C++11)

Capacity

multiset::empty

multiset::size

multiset::max_size

Modifiers

multiset::clear

multiset::insert

multiset::emplace (C++11)

multiset::emplace_hint (C++11)

multiset::erase

multiset::swap

multiset::extract (C++17)

multiset::merge (C++17)

Lookup

multiset::count

multiset::find

multiset::contains (C++20)

multiset::equal_range

multiset::lower_bound

multiset::upper_bound

Observers

multiset::key_comp

multiset::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::multiset<int> contains any elements:

Run this code

#include <set>
#include <iostream>
 
int main()
{
    std::multiset<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)