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

• Difficulty Level : Basic
• Last Updated : 17 Jun, 2020

Sets are a type of associative containers in which each element has to be unique, because the value of the element identifies it. The value of the element cannot be modified once it is added to the set, though it is possible to remove and add the modified value of that element.

set::empty()

empty() function is used to check if the set container is empty or not.

Syntax :

setname.empty()
Parameters :
No parameters are passed.
Returns :
True, if set is empty
False, Otherwise

Examples:

Input  : myset{1, 2, 3, 4, 5};
myset.empty();
Output : False

Input  : myset{};
myset.empty();
Output : True

Errors and Exceptions

1. It has a no exception throw guarantee.
2. Shows error when a parameter is passed.

 // INTEGER SET// CPP program to illustrate// Implementation of empty() function#include #include using namespace std;  int main(){    // set declaration    set myset{};      // checking if set is empty    if (myset.empty()) {        cout << "True";    }    else {        cout << "False";    }    return 0;}

Output:

True

 // CHARACTER SET// CPP program to illustrate// Implementation of empty() function#include #include using namespace std;  int main(){    // set declaration    set myset{ 'A', 'b' };      // checking if set is empty    if (myset.empty()) {        cout << "True";    }    else {        cout << "False";    }

Output:

False

Time Complexity : O(1)

Application :
Given a set of integers, find the sum of the all the integers.

Input  : 1, 5, 6, 3, 9, 2
Output : 26
Explanation -  1+5+6+3+9+2 = 26

Algorithm

1. Check if the set is empty, if not add the first element to a variable initialised as 0, and erase the first element.
2. Repeat this step until the set is empty.
3. Print the final value of the variable.

 // CPP program to illustrate// Application of empty() function#include#include   using namespace std;   int main(){    // sum variable declaration    int sum = 0;       // set declaration    set myset{ 1, 5, 6, 3, 9, 2 };       // finding sum of elements    while(!myset.empty()){        sum+= *myset.begin();        myset.erase(myset.begin());    }          // print sum     cout<

Output:

26

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