C++ set empty
The empty function in C++ is utilized to determine if the set container is devoid of elements. It will provide a true boolean value if the set container has a size of 0, otherwise, it will return false.
Syntax
bool empty() const; // until C++ 11
bool empty const noexcept; //since C++ 11
Parameter
Return value
It returns true when the set container is devoid of elements (size equals 0); otherwise, it returns false.
Complexity
Constant.
Iterator validity
No changes.
Data Races
The container is accessed.
Simultaneously retrieving the elements of a set is considered to be a secure operation.
Exception Safety
This function never throws exception.
Example 1
Let's examine a straightforward example to verify whether a set includes any elements or not:
#include <set>
#include <iostream>
using namespace std;
int main()
{
set<int> numbers;
cout << " Initially, numbers.empty(): " << numbers.empty() << "\n";
numbers = {100, 200, 300};
cout << "\n After adding elements, numbers.empty(): " << numbers.empty() << "\n";
}
Output:
Initially, numbers.empty(): 1
After adding elements, numbers.empty(): 0
In the example given, when the set is initially empty with a size of 0, the empty function will return true. However, after adding elements to the set, the function will return false.
Example 2
Let's examine a basic example to verify if a set is empty or not:
#include <iostream>
#include <set>
using namespace std;
int main(void) {
set<char> s;
if (s.empty())
cout << "Set is empty." << endl;
s = {100};
if (!s.empty())
cout << "Set is not empty." << endl;
return 0;
}
Output:
Set is empty
Set is not empty
If the aforementioned example uses a conditional statement, when the set is devoid of elements, it will output "set is empty". Conversely, upon adding elements, it will output "set is not empty".
Example 3
Let's see a simple example:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<int> myset;
myset = {100, 200, 300};
while (!myset.empty())
{
cout << *myset.begin()<< '\n';
myset.erase(*myset.begin());
}
return 0;
}
Output:
100
200
300
It employs the empty function within a while loop to display the elements of a set until the set is no longer empty.
Example 4
Let's see a simple example:
#include <iostream>
#include <set>
#include <string>
using namespace std;
int main() {
typedef set<int> phoneSet;
int number;
phoneSet phone;
if (phone.empty())
cout << "Set 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 set
}
if (!phone.empty())
{
cout<<"\nList of telephone numbers: \n";
phoneSet::iterator p;
for(p = phone.begin(); p!=phone.end(); p++)
{
cout<<(*p)<<" \n ";
}
}
return 0;
}
Output:
Set is empty. Please insert content!
Enter three sets of number:
1111
5555
3333
List of telephone numbers:
1111
3333
5555
In the previous illustration, the software initially generates a phone collection interactively containing three sets of numbers. It subsequently verifies whether the collection is devoid of any entries. Should the collection be empty, a notification is shown; otherwise, it exhibits all the telephone numbers contained within the collection.
