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std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::empty - cppreference.com

From cppreference.com

bool empty() const noexcept;

 (since C++11)

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

Return value

true if the container is empty, false otherwise.

Complexity

Constant.

Example

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

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

returns the number of elements
(public member function) [edit]
checks whether the container is empty
(function template) [edit]