std::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().

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// 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;
}

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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 descending order. This function does a comparison in a way that puts greater element before.

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// 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;
}

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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. This “comparator” function returns a value; convertible to bool, which basically tells us whether the passed “first” argument should be placed before the passed “second” argument or not.
For eg: In the code below, suppose intervals {6,8} and {1,9} are passed as arguments in the “compareInterval” function(comparator function). Now as i1.first (=6) > i2.first (=1), so our function returns “false”, which tells us that “first” argument should not be placed before “second” argument and so sorting will be done in order like {1,9} first and then {6,8} as next.

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// A C++ program to demonstrate STL sort() using
// our own comparator
#include<bits/stdc++.h>
using namespace std;
  
// An interval has a 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;
}

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Output:

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

This article is contributed by Shubham Agrawal. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above



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Improved By : rahuku, AbhishekSharma5