upper_bound() in C++ STL

The C++ Standard Library consists of the header, <algorithm> which defines a collection of functions (principally designed to deal with a range of elements). upper_bound() is a method in the STL that returns an iterator pointing to the first element in the range which compares greater than a certain value. The method returns the last iterator if no element compares greater than the value.

Syntax:

upper_bound( iterator_begin, iterator_end, val );

Parameters: The upper_bound() method accepts 3 parameters

  • iterator_begin: Iterator to the initial position
  • iterator_end: Iterator to the final position ( Note: the range is [iterator_begin,iterator_end) )
  • val: Value of the upper bound to search for in the range

Return value: An iterator to the upper bound of val in the range. iterator_end if no elements compare more than val

Example of upper_bound() method

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;


int main()
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(5);
    v.push_back(5);
    v.push_back(5);
    v.push_back(5);
    v.push_back(6);

    vector<int>::iterator it = upper_bound(v.begin(), v.end(), 5);
    cout<<"Upper bound of element 5 is: "<< distance(v.begin(), it) << endl;
}

Output:

Upper bound of element 5 is: 6

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