C++ multiset empty()

C++ Multiset empty() function is used to check whether the multiset container is empty or not. It returns true if the multiset container is empty (size is 0) otherwise, it returns false.

Syntax

bool empty() const;               // until C++ 11

bool empty const noexcept;    //since C++ 11

Parameter

None

Return value

The empty() function returns true if the multiset container is empty (size is 0) otherwise, it returns false.

Complexity

Constant.

Iterator validity

No changes.

Data Races

The container is accessed.

Concurrently accessing the elements of multiset is safe.

Exception Safety

This function never throws exception.

Example 1

Let's see the simple example to check if a multiset contains any element or not:

#include <set>
#include <iostream>

using namespace std;

int main()
{
    multiset<int> numbers;
    cout << " Initially, numbers.empty(): " << numbers.empty() << "\n";
    numbers = {100, 200, 300, 200};
    cout << "\n After adding elements, numbers.empty(): " << numbers.empty() << "\n";
}

Output:

 Initially, numbers.empty(): 1

 After adding elements, numbers.empty(): 0

In the above example, initially size of multiset is 0 hence, empty() function returns 1 (true) and after adding elements it returns 0 (false).

Example 2

Let's see a simple example to check whether multiset is empty or not:

#include <iostream>
#include <set>

using namespace std;

int main(void) {

   multiset<char> s;

   if (s.empty())
      cout << "Multiset is empty." << endl;

   s = {100};

   if (!s.empty())
      cout << "Multiset is not empty." << endl;

   return 0;
}

Output:

Multiset is empty
Multiset is not empty

In the above example, if condition statement is used. If multiset is empty it will return multiset is empty after adding elements it will return multiset is not empty.

Example 3

Le's see a simple example:

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  multiset<int> mymultiset;

  mymultiset = {100, 300, 300, 200, 400, 400};

  while (!mymultiset.empty())
  {
    cout << *mymultiset.begin()<< '\n';
    mymultiset.erase(*mymultiset.begin());
  }

  return 0;
}

Output:

In the above example, It simply uses the empty() function in while loop and prints the elements of multiset until the multiset is not empty.

Example 4

Let's see a simple example:

#include <iostream>
#include <set>
#include <string>

using namespace std;

int main() {

  typedef multiset<int> phoneMultiset;
   
   int number;
   phoneMultiset phone;
   
   if (phone.empty())
      cout << "Multiset is empty. Please insert content! \n " << endl;
   
   cout<<"Enter three sets of number: \n";
   
   for(int i =0; i<3; i++)
   {
       cin>> number;    // Get value
       phone.insert(number);   // Put them in multiset
   }

   if (!phone.empty())
   {
      cout<<"\nList of telephone numbers: \n";
      phoneMultiset::iterator p;
      for(p = phone.begin(); p!=phone.end(); p++)
      {
          cout<<(*p)<<" \n ";
      }
   }
   return 0;
}

Output:

Multiset is empty. Please insert content! 
 
Enter three sets of number: 
10002
10002
10003

List of telephone numbers: 
10002 
10002 
10003

In the above example, the program first creates phone multiset interactively with three multiset of numbers. Then it checks if the multiset is empty or not. If multiset is empty, then it displays a message otherwise, it displays all the telephone numbers available in the multiset.

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