C++ Unordered_map::empty() Function

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The C++ unordered_map::empty() functionis 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