C++ unordered_map - empty() Function

The C++ unordered_map::empty function is used to check whether the unordered_map is empty or not. It returns true if the size of the unordered_map is zero, else returns false.

Syntax

C++11

bool empty() const noexcept;

Parameters

No parameter is required.

Return Value

true if the size of the unordered_map is zero, else returns false.

Time Complexity

Constant i.e, Θ(1).

Example:

In the example below, the unordered_map::empty function is used to check whether the unordered_map is empty or not.

#include <iostream>
#include <unordered_map>
using namespace std;
 
int main (){
  unordered_map<int, string> uMap;

  cout<<boolalpha;

  cout<<"Is the Unordered Map empty?: "<<uMap.empty()<<"\n";

  cout<<"Add key/element pairs in the Unordered Map.\n";

  uMap[101] = "John";
  uMap[102] = "Marry";
  uMap[103] = "Kim";

  cout<<"Now, Is the Unordered Map empty?: "<<uMap.empty()<<"\n";
  return 0;
}

The output of the above code will be:

Is the Unordered Map empty?: true
Add key/element pairs in the Unordered Map.
Now, Is the Unordered Map empty?: false

❮ C++ <unordered_map> Library