std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::empty (3) - Linux Manuals

std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::empty: std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::empty

NAME

std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::empty - std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::empty

Synopsis


bool empty() const noexcept; (since C++11)
                                            (until C++20)
[[nodiscard]] bool empty() const noexcept; (since C++20)


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

Parameters


(none)

Return value


true if the container is empty, false otherwise

Complexity


Constant.

Example


The following code uses empty to check if a std::unordered_map<int,int> contains any elements:
// Run this code


  #include <unordered_map>
  #include <iostream>
  #include <utility>


  int main()
  {
      std::unordered_map<int, int> numbers;
      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(): 1
  After adding elements, numbers.empty(): 0

See also


     returns the number of elements
size (public member function)

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