In C++, the set upper_bound() is a built-in method used to find the first element in the set that is just greater than the given value. In this article, we will learn about set upper_bound() function in C++.

Let’s take a quick look at a simple illustration of the function:

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

int main() {

    set<int> s = {1, 3, 5, 6, 7};

    // Finding  upper bound of 3
    cout << *s.upper_bound(3);
  
    return 0;
}

5

Explanation: In the above code, we found the upper bound 5 which is just greater than 3 in the given set s.

This article covers the syntax, usage, and common examples of set upper_bound() method in C++:

Syntax of set upper_bound()

The set upper_bound() is the member method of std::set class defined inside <set> header file.

s.upper_bound(k);

Parameters

• k: Value whose upper bound is to be searched.

Return Value

• Returns an iterator to the first element that is just greater than the given value.
• If all the elements are less than or equal to the given value, returns iterator to the end.

Examples of upper_bound()

The following examples demonstrate the use of set upper_bound() function in different cases.

Find Upper Bound in Set of Strings

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

int main() {
    set<string> s = {"hello", "geeks",
                     "welcome"};

    // Finding upper bound of string "hello"
    cout << *s.upper_bound("hello");

    return 0;
}

welcome

Find Not Existing Upper Bound

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

int main() {
    set<int> s = {1, 5, 3, 7, 6};

    // Finding upper bound of 7 in s
    auto it = s.upper_bound(7);
    if (it != s.end())
        cout << *it;
    else
        cout << "Upper Bound Not Exists.";
    return 0;
}

Upper Bound Not Exists.

Explanation: In the above code, we are trying to find the upper bound of 7 and all the elements are less than or equal to the 7 in the set container. Hence the upper bound of 7 does not exist in the given set container.

Check if an Element Exists in the Set

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

int main() {
    set<int> s = {1, 5, 3, 7, 6};

    // Finding upper bound of 7 in s
    auto it = --s.upper_bound(7);
    if (*it == 7)
        cout << "Exists.";
    else
        cout << "Not Exists.";
    return 0;
}

Exists.

Explanation: As set is sorted, if the given value exists in the set, the set upper_bound() will return the iterator to the element next to the given element. This iterator can be decremented to point to the given element in the set.