compare function in sort c++ stl

// A C++ program to sort vector using 
// our own comparator 
#include <bits/stdc++.h> 
using namespace std; 
  
// An interval has start time and end time 
struct Interval { 
    int start, end; 
}; 
  
// Compares two intervals according to staring times. 
bool compareInterval(Interval i1, Interval i2) 
{ 
    return (i1.start < i2.start); 
} 
  
int main() 
{ 
    vector<Interval> v { { 6, 8 }, { 1, 9 }, { 2, 4 }, { 4, 7 } }; 
  
    // sort the intervals in increasing order of 
    // start time 
    sort(v.begin(), v.end(), compareInterval); 
  
    cout << "Intervals sorted by start time : \n"; 
    for (auto x : v) 
        cout << "[" << x.start << ", " << x.end << "] "; 
  
    return 0; 
}