std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::empty

 

C++

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Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

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forward_list (C++11)

list

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map

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unordered_set (C++11)

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unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

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flat_set (C++23)

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flat_map (C++23)

flat_multimap (C++23)

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span (C++20)

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std::flat_map

Member types

Member functions

flat_map::flat_map flat_map::operator= Element access flat_map::at flat_map::operator[] Iterators flat_map::beginflat_map::cbegin flat_map::endflat_map::cend flat_map::rbeginflat_map::crbegin flat_map::rendflat_map::crend Lookup flat_map::count flat_map::find flat_map::contains flat_map::equal_range    flat_map::lower_bound flat_map::upper_bound Capacity flat_map::size flat_map::max_size flat_map::empty Modifiers flat_map::clear flat_map::erase flat_map::swap flat_map::emplace flat_map::extract flat_map::replace flat_map::insert flat_map::insert_range flat_map::insert_or_assign flat_map::emplace_hint flat_map::try_emplace Observers flat_map::key_comp flat_map::keys flat_map::value_comp flat_map::values

Non-member functions

operator==operator<=>         swap(std::flat_map) erase_if(std::flat_map)

Helper classes

uses_allocator<std::flat_map>

Tags

sorted_unique       sorted_unique_t

Deduction guides

 

bool empty() const noexcept;		(since C++23)

Checks if the underlying containers have no elements. Equivalent to: return begin() == end();.

Parameters

(none)

Return value

true if the underlying containers are empty, false otherwise.

Complexity

Constant.

Example

The following code uses empty to check if a std::flat_map<int, int> contains any elements:

Run this code

#include <iostream>
#include <flat_map>
#include <utility>
 
int main()
{
    std::flat_map<int,int> numbers;
    std::cout << std::boolalpha;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
 
    numbers.emplace(42, 13);
    numbers.insert(std::make_pair(13317, 123));
    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)