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C++ Unordered_multimap::empty() Function
The C++ std::unordered_multimap::empty() function is used to check whether unordered_multimap is empty or not. If the unordered_multimap is empty, then it returns true; otherwise, it returns false. This function does not modify or change the content of the container in any way.
Syntax
Following is the syntax of std::unordered_multimap::empty() function.
bool empty() const noexcept;
Parameters
This function does not accepts any parameters.
Return value
This function returns boolean values, i.e.true if unordered_multimap is empty (size zero) otherwise false.
Example 1
Let's look at the following example, where we are going to demonstrate the usage of unordered_multimap::empty() function.
#include <iostream> #include <unordered_map> using namespace std; int main(void) { unordered_multimap<char, int> umm; if (umm.empty()) cout << "Unordered multimap is empty." << endl; umm.emplace_hint(umm.begin(), 'a', 1); umm.emplace_hint(umm.end(), 'b', 2); if (!umm.empty()) cout << "Unordered multimap is not empty." << endl; return 0; }
Output
Let us compile and run the above program, this will produce the following result −
Unordered multimap is empty. Unordered multimap is not empty.
Example 2
Consider the following example, where we are going to use the empty() function to check if an unordered_multimap contains any elements or not.
#include <unordered_map> #include <iostream> #include <utility> using namespace std; int main() { unordered_multimap<int, int> numbers; cout << boolalpha; cout << "Initially, numbers.empty(): " << numbers.empty() << '\n'; numbers.emplace(55, 110); numbers.insert(make_pair(12345, 115)); cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n'; }
Output
If we run the above code it will generate the following output −
Initially, numbers.empty(): true After adding elements, numbers.empty(): false
Example 3
In the following example, we are going to use the empty() function and display all the elements in the container if it was not empty.
#include <unordered_map> #include <iostream> #include <utility> using namespace std; int main() { unordered_multimap<string, int> marks_of_students; marks_of_students.insert(make_pair("Aman", 100)); marks_of_students.insert(make_pair("Akash", 95)); marks_of_students.insert({{"Vivek", 98},{"Aman", 92},{"Akash", 97},{"Rahul", 96}}); for(auto & it: marks_of_students){ if(marks_of_students.empty()){ cout<<"marks of students are empty, I can't be able to fetch the data!"<<endl; } else{ cout<<"Marks of "<<it.first<<" is "<<it.second<<endl; } } cout<<endl; return 0; }
Output
Following is the output of the above code −
Marks of Rahul is 96 Marks of Vivek is 98 Marks of Akash is 97 Marks of Akash is 95 Marks of Aman is 92 Marks of Aman is 100