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set::empty() function in C++ STL

C++ STL set::empty() function: Here, we are going to learn about the empty() function of set in C++ STL (Standard Template Library).
Submitted by Radib Kar, on February 16, 2019

C++ STL set::empty() function

set::empty() function is a predefined function, it is used to check whether a set is empty or not. If set is empty it returns true (1), if set is not empty it returns false (0).

Syntax

set<T> st; //declaration
set<T>::iterator it; //iterator declaration
st.empty(); 

Parameter(s)

This function does not accept any parameter.

Return value

This function returns a Bool (True or False) value.

Usage: The function checks whether the set is empty or not.

Sample Input and Output

For a set of integer,
set<int> st;
st.insert(4);
st.insert(5);
set content:
    4
    5

Bool check=st.empty();  
check =False

St.erase(st.begin()); //erases 4
St.erase(st.begin()); //erases 5
Set content:
Empty set 
    
//now check again
check=st.empty()
check=TRUE

Header file

Header file to be included:

#include <iostream>
#include <set>
OR
#include <bits/stdc++.h>

Example

#include <bits/stdc++.h>
using namespace std;

void printSet(set<int> st) {
  set<int>::iterator it;
  cout << "Set contents are:\n";
  for (it = st.begin(); it != st.end(); it++) cout << *it << " ";
  cout << endl;
}

int main() {
  cout << "Example of empty function\n";
  set<int> st;
  set<int>::iterator it;
  cout << "inserting 4\n";
  st.insert(4);
  cout << "inserting 6\n";
  st.insert(6);
  cout << "inserting 10\n";
  st.insert(10);

  printSet(st);  // printing current set

  if (st.empty())
    cout << "It's empty\n";
  else
    cout << "It's not empty\n";

  cout << "erasing all elements\n";
  st.clear();

  if (st.empty())
    cout << "It's empty\n";
  else
    cout << "It's not empty\n";

  return 0;
}

Output

Example of empty function
inserting 4
inserting 6
inserting 10
Set contents are:
4 6 10
It's not empty
erasing all elements
It's empty