std::set::empty

 

C++

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)

Technical Specifications

 

Containers library

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

 

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::emplace (C++11)

set::emplace_hint (C++11)

set::erase

set::swap

Lookup

set::count

set::find

set::equal_range

set::lower_bound

set::upper_bound

Observers

set::key_comp

set::value_comp

 

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

See also

size	returns the number of elements (public member function)