std::unordered_map::empty

1	`bool` `empty()` `const;`

(since C++11)

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

Parameters

(none).

Return value

true if the container is empty, false otherwise.

Exceptions

noexcept specification:

noexcept

Complexity

Constant.

Example

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

#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