sort() in C++ STL

We have discussed qsort() in C. C++ STL provides a similar function sort that sorts a vector or array (items with random access). Below is a simple program to show working of sort().

// C++ program to demonstrate default behaviour of // sort() in STL. #include <bits/stdc++.h> using namespace std;   int main() {     int arr[] = {1, 5, 8, 9, 6, 7, 3, 4, 2, 0};     int n = sizeof(arr)/sizeof(arr[0]);       sort(arr, arr+n);       cout << "\nArray after sorting using "          "default sort is : \n";     for (int i = 0; i < n; ++i)         cout << arr[i] << " ";       return 0; }

Output :

Array after sorting using default sort is : 
0 1 2 3 4 5 6 7 8 9 

So by default, sort() sorts an array in ascending order.

How to sort in descending order?
sort() takes a third parameter that is used to specify the order in which elements are to be sorted. We can pass “greater<>()” function to sort in increasing order. This function does comparison in a way that puts greater element before.

// C++ program to demonstrate descending order sort using // greater<>(). #include <bits/stdc++.h> using namespace std;   int main() {     int arr[] = {1, 5, 8, 9, 6, 7, 3, 4, 2, 0};     int n = sizeof(arr)/sizeof(arr[0]);       sort(arr, arr+n, greater<int>());       cout << "Array after sorting : \n";     for (int i = 0; i < n; ++i)         cout << arr[i] << " ";       return 0; }

Output:

Array after sorting : 
9 8 7 6 5 4 3 2 1 0 

How to sort in particular order?
We can also write our own comparator function and pass it as a third parameter.

// A C++ program to demonstrate STL sort() 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() {     Interval arr[] =  { {6,8}, {1,9}, {2,4}, {4,7} };     int n = sizeof(arr)/sizeof(arr[0]);       // sort the intervals in increasing order of     // start time     sort(arr, arr+n, compareInterval);       cout << "Intervals sorted by start time : \n";     for (int i=0; i<n; i++)        cout << "[" << arr[i].start << "," << arr[i].end             << "] ";       return 0; }

Output:

Intervals sorted by start time : 
[1,9] [2,4] [4,7] [6,8]