C++ std::sort() Usage

What Will You Learn in This Guide?

In this guide, you'll learn how the std::sort() function in C++ works, what algorithm it uses, and how you can sort arrays ascending, descending, or by a special rule.
You'll test code with examples and explore advanced techniques like std::greater, lambda expressions, and custom functions.

What is std::sort() and How Does It Work?

std::sort() is a built-in function in the C++ Standard Library (<algorithm>) that is used to sort data structures (e.g. arrays or vectors) in a specific order.

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

first → Beginning of the range to be sorted

last → Address showing the next element after the last element

comp → (optional) Comparison function. If not entered, std::less<T>() is used by default (ascending order).

• Algorithm used: std::sort() uses Introsort, a hybrid technique (mixture of Quick Sort + Heap Sort + Insertion Sort). Its complexity is average and in the worst case O(N log N).

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1. Sort Ascending (Default)

By default, std::sort() sorts arrays in ascending order.

#include <iostream>
#include <algorithm>
using namespace std;

int main() {
    int sayilar[] = {50, 40, 30, 20, 10};
    int uzunluk = sizeof(sayilar)/sizeof(sayilar[0]);

    std::sort(sayilar, sayilar + uzunluk); // Artan sıralama

    for (int i = 0; i < uzunluk; i++)
        cout << sayilar[i] << " ";
}

• Description:

If the third parameter is not specified, std::less<int>() is used and sorts the array from smallest to largest.

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2. Sort in Descending Order

For descending sorting, the third parameter is given the function std::greater<int>() or lambda.

Method 1 – std::greater<int>()

int sayilar[] = {44, 22, 55, 33, 66};
std::sort(sayilar, sayilar + 5, greater<int>()); // Büyükten küçüğe

Method 2 – Lambda Function

std::sort(sayilar, sayilar + 5, [](int a, int b){ return a > b; });

Note:

Both methods give the same result — they sort the array in descending order.

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3. Custom Sort (User Defined)

You can also define your own comparison rule. In the example below, we sort the array by remainder after division by 10:

#include <iostream>
#include <algorithm>
using namespace std;

bool kalanGoreSırala(int a, int b) {
    return (a % 10) < (b % 10);
}

int main() {
    int sayilar[] = {18, 45, 34, 92, 21};
    std::sort(sayilar, sayilar + 5, kalanGoreSırala);
    for (int s : sayilar) cout << s << " ";
}

• Description:

The element with the smallest value (a 10%) is brought forward. Result: 21, 92, 34, 45, 18.

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Performance and Complexity

Feature	Description
Algorithm	Introsort (combination of Quick Sort + Heap Sort + Insertion Sort)
Average Complexity	O(N log N)
Worst Case	O(N log N)
Stability (stable)	No — items with the same values ​​can be swapped after sorting

If stable sorting is required:

You can use std::stable_sort() function.

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Frequently Asked Questions (FAQ)

1. Does std::sort() only work on arrays?

No, it also works with random access structures like std::vector and std::deque.

2. What is the difference with qsort()?

std::sort() is a type-safe, modern version of C++. qsort() belongs to the C language and works with void* pointers.

3. Can I also sort strings?

Yes, you can sort std::string or char arrays as well.

4. Why should I return bool?

The comparator function specifies true/false which of the two elements should come first.

5. Why is std::sort() not stable?

The order of elements with the same value is not preserved. So std::stable_sort() is recommended if stability is required.

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Result

In this guide, we examined the C++ std::sort() function from basic to advanced level. You can sort by ascending, descending or special rules; You can customize it with lambda expressions. Thanks to the Introsort algorithm, your rankings will be fast, reliable and flexible.

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