C++ multiset clear
The clear method in C++ for multimultisets is employed to eliminate all elements from the container. This action resets the multimultiset, reducing its size to zero.
Syntax
void clear(); //until C++ 11
void clear() noexcept; //since C++ 11
Parameter
Return value
Complexity
Linear in size.
Iterator validity
All pointers, references, and iterators associated with this container become invalid.
Data Races
The container is modified.
All contained elements are modified.
Exception Safety
This function never throws exception.
Example 1
Let's explore a basic example to determine the cardinality of a multiset before and after executing the clear operation:
#include <iostream>
#include <set>
using namespace std;
int main() {
multiset<int> mymultiset = {10,20,20,30};
cout << "Initial size of multiset before clear operation = " << mymultiset.size() << endl;
mymultiset.clear();
cout << "Size of multiset after clear operation = " << mymultiset.size() << endl;
return 0;
}
Output:
Initial size of multiset before clear operation = 4
Size of multiset after clear operation = 0
After initializing the multiset with four elements in the example above, the size is set to 4. However, following the clear operation, the size is reset to 0.
Example 2
Let's examine a straightforward illustration to clarify the components of the multiset:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
multiset<string> mymultiset;
mymultiset = {"Nikita","Deep","Aman"};
cout << "mymultiset contains:\n";
for (multiset<string>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
cout << *it<< '\n';
mymultiset.clear();
mymultiset= {"Deep", "Raaz"};
cout << "\nmymultiset contains:\n";
for (multiset<string>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
cout << *it<< '\n';
return 0;
}
Output:
mymultiset contains:
Aman
Deep
Nikita
mymultiset contains:
Deep
Raaz
After emptying the multiset as shown above, new elements can be added without the need for initialization.
Example 3
Let's examine a basic illustration to clarify the components of the multiset:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
int n;
multiset<string> m1,m2,m3;
m1 = {"Hello", "World"};
m2 = {"Java", "Program"};
m3 = {"C++", "Coding"};
cout << "m1 group has following members:\n";
for (multiset<string>::iterator it=m1.begin(); it!=m1.end(); ++it)
cout << *it << ' ';
cout << "\n\nm2 group has following members:\n";
for (multiset<string>::iterator it=m2.begin(); it!=m2.end(); ++it)
cout << *it<< ' ';
cout << "\n\nm3 group has following members:\n";
for (multiset<string>::iterator it=m3.begin(); it!=m3.end(); ++it)
cout << *it<< ' ';
cout<<"\n\nWhich group do you want to delete?\n 1.m1\n 2.m2\n 3.m3\n Please enter your choice: ";
cin>>n;
if(n==1){
m1.clear();
cout<<"\nGroup m1 has been cleared.";
}
else if(n==2){
m2.clear();
cout<<"\nGroup m2 has been cleared.";
}
else if(n==3){
m3.clear();
cout<<"\nGroup m3 has been cleared.";
}
else
cout<<"Invalid option!";
return 0;
}
Output:
m1 group has following members:
Hello World
m2 group has following members:
Java Program
m3 group has following members:
C++ Coding
Which group do you want to delete?
1.m1
2.m2
3.m3
Please enter your choice: 2
Group m2 has been cleared.
In the scenario described, there are three sets of multiset elements, and based on the user's selection, one of these sets is removed.
Example 4
Let's see a simple example:
#include <iostream>
#include <set>
using namespace std;
int main() {
int n;
multiset<string> fruit = {"Banana","Apple","Orange","Banana"};
cout << "Fruit bucket has following fruits = \n";
for (multiset<string>::iterator it=fruit.begin(); it!=fruit.end(); ++it)
cout << *it<< '\n';
cout<<"\nDo you want to clear your fruit bucket?\nPress 1 for Yes and 0 for No: ";
cin>>n;
if( n==1){
fruit.clear();
cout<<fruit.size()<<" fruits in bucket \n";
}
else if(n==0)
cout <<fruit.size() << " fruits in bucket \n" ;
return 0;
}
Output:
1.
Fruit bucket has following fruits =
Apple
Banana
Banana
Orange
Do you want to clear your fruit bucket?
Press 1 for Yes and 0 for No: 1
0 fruits in bucket
2.
Fruit bucket has following fruits =
Apple
Banana
Banana
Orange
Do you want to clear your fruit bucket?
Press 1 for Yes and 0 for No: 1
4 fruits in bucket
In the given scenario, a fruit multiset is created with three different types of fruits. To clear the multiset, inputting 0 will result in the fruit bucket containing 4 elements, while entering 1 will clear the fruit multiset entirely, reducing its size to 0.
