multiset_name.size()

// CPP program to demonstrate the
// multiset::size() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
   
      multiset<int> s;
   
      // Function to insert elements
      // in the multiset container
      s.insert(10);
      s.insert(13);
   
      cout << "The size of multiset: " << s.size();
      s.insert(13);
      s.insert(25);
   
      cout << "\nThe size of multiset: " << s.size();
      s.insert(24);
   
      cout << "\nThe size of multiset: " << s.size();
      return 0;
}

multiset的大小：2
multiset的大小：4
multiset的大小：5

// CPP program to demonstrate the
// multiset::size() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
   
      multiset<int> s;
   
      cout << "The size of multiset: " << s.size();
      s.insert(2);
      s.insert(3);
   
      cout << "\nThe size of multiset: " << s.size();
      s.insert(4);
   
      cout << "\nThe size of multiset: " << s.size();
      return 0;
}

multiset的大小：0
multiset的大小：2
multiset的大小：3