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set::size() in C++ STL

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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.

The set class provides a member function, set::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.

Errors and Exceptions

  • It has a no exception throw guarantee.
  • Shows an 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

Note: This function works in constant time complexity.

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Last Updated : 30 May, 2023
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