C++ Unordered_map Library - empty() Function

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Description

The C++ function std::unordered_map::empty() tests whether unordered_map is empty or not. Unordered_map of size zero is considered as empty unordered_map.

Declaration

Following is the declaration for std::unordered_map::empty() function form std::unordered_map header.

C++11

bool empty() const noexcept;

Parameters

None

Return value

Returns true if map is empty otherwise false.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::unordered_map::empty() function.

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_map<char, int> um;

   if (um.empty())
      cout << "Unordered map is empty" << endl;

   um.emplace('a', 1);

   if (!um.empty())
      cout << "Unordered map is not empty" << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Unordered map is empty
Unordered map is not empty