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

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Symbols index

External libraries

 

Containers library

node-handle (C++17)

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vector

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multimap

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unordered_set (C++11)

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unordered_map (C++11)

unordered_multimap (C++11)

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stack

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flat_multimap (C++23)

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std::multimap

Member functions

multimap::multimap multimap::~multimap        multimap::operator= multimap::get_allocator

Iterators multimap::beginmultimap::cbegin (C++11) multimap::endmultimap::cend (C++11) multimap::rbeginmultimap::crbegin (C++11)    multimap::rendmultimap::crend (C++11) Capacity multimap::size multimap::max_size multimap::empty Observers multimap::key_comp multimap::value_comp Modifiers multimap::clear multimap::insert multimap::erase multimap::swap multimap::merge (C++17) multimap::insert_range (C++23) multimap::emplace (C++11) multimap::emplace_hint (C++11) multimap::extract (C++17) Lookup multimap::count multimap::find multimap::contains (C++20) multimap::equal_range multimap::lower_bound multimap::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::multimap) erase_if(std::multimap) (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::multimap<int, int> contains any elements:

Run this code

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

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