set::size() in C++ STL

Sets are containers that store unique elements following a specific order. Internally, the elements in a set are always sorted. Sets are typically implemented as binary search trees.

size() function is used to return the size of the set container or the number of elements in the set container.



Return Value: It returns the number of elements in the set container.


Input  : set1{'a', 'b', 'c', 'd'};
Output : 4

Input  : set2{};
Output : 0

Errors and Exceptions

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

// C++ program to illustrate
// size() function on set
#include <bits/stdc++.h>
using namespace std;
int main()
    // Take any two sets
    set<char> set1, set2;
    for (int i = 0; i < 4; i++) {
        set1.insert('a' + i);
    // Printing the size of sets
    cout << "set1 size: " << set1.size();
    cout << endl;
    cout << "set2 size: " << set2.size();
    return 0;


set1 size: 4
set2 size: 0

Time complexity: Constant

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