Sort in C++ STL

July 22, 2023

About Sorting in STL

The C++ Standard Template Library (STL) is a powerful collection of template classes and functions that offer generic algorithms to manipulate data containers effortlessly. STL includes several efficient sorting algorithms, making it a popular choice among C++ programmers.
sorting in stl

Sorting Algorithms in C++ STL

C++ STL offers multiple sorting algorithms to cater to different use cases. Let’s explore some of the most commonly used ones:
  • std::sort()
The `std::sort()` function is the most basic sorting algorithm in C++ STL. It uses a variant of the intro sort algorithm, which combines quicksort, heapsort, and insertion sort. The efficient algorithm often outperforms other sorting techniques for most data sets.
  • std::stable_sort()
If the order of equal elements needs to be preserved during sorting, `std::stable_sort()` is the ideal choice. It employs a stable sorting algorithm, typically based on merge sort, ensuring the relative order of equivalent elements remains unchanged.
  • std::partial_sort()
The `std::partial_sort()` function partially sorts a container by placing the first N elements in sorted order. The remaining elements are not guaranteed to be in any specific order but will be greater than the sorted part.
  • std::nth_element()
When finding the N-th element in a container without thoroughly sorting it, `std::nth_element()` comes in handy. It rearranges the elements such that the N-th element is sorted, with all aspects before it being less than or equal and all elements after it being greater than or equal.
  • std::make_heap() and std::sort_heap()
These functions help create and sort heaps, respectively. A heap is a specialized data structure that allows efficient access to the maximum or minimum element.

Syntax of Sort() :

sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

The function doesn’t produce a result. Just the items/elements from the first to the last iterations  are updated. The third parameter, comp, must be a function that establishes the hierarchy of the components to be sorted in. If nothing else is supplied, the sorting happens in ascending order.

Example of Sorting in Ascending Order :

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

int main() {
    vector arr;
    arr.push_back(34);
    arr.push_back(70);
    arr.push_back(20);
    arr.push_back(56);
    arr.push_back(1);
    
     cout<<"The element of array before sorting : ";
    for(int i=0;i < arr.size();i++){
         cout<< arr[i]<<" ";
    }
    cout<< endl;
    // sort function to sorting the elements
    sort(arr.begin(), arr.end());   
    cout<<"The element of array after sorting : ";
    for(int i=0;i < arr.size();i++){
         cout<< arr[i]<<" ";
    }
   
    return 0;
}

Output :

The element of array before sorting : 34 70 20 56 1 
The element of array after sorting : 1 20 34 56 70

In the above program, we take the array and used sort function to sort the elements in ascending order as comparator is not used , by default elements are arranged in ascending order.

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Example of Sorting in Descending Order:

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

int main() {
    vector arr;
    arr.push_back(34);
    arr.push_back(70);
    arr.push_back(20);
    arr.push_back(56);
    arr.push_back(1);
    
     cout<<"The element of array before sorting : ";
    for(int i=0;i< arr.size();i++){
         cout<< arr[i]<<" ";
    }
    cout<());   
    cout<<"The element of array after sorting : ";
    for(int i=0;i< arr.size();i++){
         cout<< arr[i]<<" ";
    }
   
    return 0;
}

Output :

The element of array before sorting : 34 70 20 56 1 
The element of array after sorting : 70 56 34 20 1

In the above program, we take the array and used sort function to sort the elements in decreasing  order as greater<int>() comparator is used to sort the elements in decreasing order

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