std::set::empty

bool empty() const;

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

Parameters

(none)

Return value

true if the container is empty, false otherwise

Exceptions

(none)	(until C++11)
`noexcept` specification: noexcept	(since C++11)

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 << "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(): 1
After adding elements, numbers.empty(): 0

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

array (C++11)
vector
deque
forward_list (C++11)
list
set
multiset
map
multimap
unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
stack
queue
priority_queue

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::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::equal_range
set::lower_bound
set::upper_bound
Observers
set::key_comp
set::value_comp