C++ Unordered_map::empty() Function

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The C++ unordered_map::empty() function is used to check whether unordered_map is empty or not. It return a boolean value true, if the size of the map is zero, otherwise it returns false, because an Unordered_map of size zero is considered an empty Unordered_map.

Syntax

Following is the syntax of unordered_map::empty() function.

unordered_map.empty();

Parameters

This function does not accepts any parameter.

Return value

This function returns boolean values, i.e., true if map is empty; otherwise, it returns false.

Example 1

Consider the following example, where we are going to demonstrate the usage of the 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;
}

Output

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

Unordered map is empty
Unordered map is not empty

Example 2

In the following example, we are going to declare a two unordered_maps, one is with the elements and another one is empty and applying the empty() function.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void){
   unordered_map<int, string> UnorderMap1, UnorderMap2;
   UnorderMap1[1] = "Tutorials";
   UnorderMap1[2] = "Points";
   UnorderMap1[3] = "Tutorix";
   if(UnorderMap1.empty())
      cout<<"true"<<endl;
   else
      cout<<"false"<<endl;
   if(UnorderMap2.empty())
      cout<<"true"<<endl;
   else
      cout<<"false"<<endl;
   return 0;
}

Output

Following is the output of the above code −

false
true

Example 3

Let's look at the following example, where we are going to display the elemets of the map using iterator if the map is not empty orelse displaying a statement.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void){
   unordered_map<int, string> UnorderMap1, UnorderMap2;
   UnorderMap1[1] = "Tutorials";
   UnorderMap1[2] = "Points";
   UnorderMap1[3] = "Tutorix";
   if(!UnorderMap1.empty())
      for (auto it = UnorderMap1.begin(); it != UnorderMap1.end(); ++it)
         cout<<it->first<<" = "<<it->second<<endl;
   else
      cout<<"Unordered map1 is empty\n";
   if(UnorderMap2.empty())
      cout<<"Unordered Map2 is empty\n";
   else
      for (auto it = UnorderMap1.begin(); it != UnorderMap1.end(); ++it)
         cout<<it->first<<" = "<<it->second<<endl;
   return 0;
}

Output

Output of the above code is as follows −

3 = Tutorix
2 = Points
1 = Tutorials
Unordered Map2 is empty