std::map<Key,T,Compare,Allocator>::empty

 

C++

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Freestanding and hosted

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Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

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Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

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Filesystem library(C++17)

Concurrency support library(C++11)

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Technical specifications

Symbols index

External libraries

 

Containers library

node-handle (C++17)

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

deque

forward_list (C++11)

list

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set

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map

multimap

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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)

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span (C++20)

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std::map

Member functions

map::map map::~map               map::operator= map::get_allocator

Element access map::at map::operator[] Iterators map::beginmap::cbegin (C++11) map::endmap::cend (C++11) map::rbeginmap::crbegin (C++11)      map::rendmap::crend (C++11) Capacity map::size map::max_size map::empty Observers map::key_comp map::value_comp Modifiers map::clear map::insert map::erase map::swap map::extract (C++17) map::merge (C++17) map::insert_range (C++23) map::insert_or_assign (C++17) map::emplace (C++11) map::emplace_hint (C++11) map::try_emplace (C++17) Lookup map::count map::find map::contains (C++20) map::equal_range map::lower_bound map::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::map) erase_if(std::map) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

Deduction guides(C++17)

 

bool empty()const;		(noexcept since C++11) (constexpr since C++26)

Checks if the container has no elements.

Return value

true if the container is empty, false otherwise.

Complexity

Constant.

Example

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

Run this code

#include <iostream>#include <map>#include <utility>   int main(){std::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)