How to Sort in Descending Order in C++: Simple Guide

To sort in descending order in C++, use std::sort with a custom comparator like std::greater<>() or a lambda function. For example, std::sort(vec.begin(), vec.end(), std::greater<>()); sorts a vector from largest to smallest.

Syntax

The std::sort function sorts elements in a range. To sort in descending order, provide a comparator that defines the order.

• std::sort(start, end, comparator); sorts elements from start to end using comparator.
• std::greater<>() is a built-in comparator that sorts in descending order.
• You can also use a lambda function like [](int a, int b) { return a > b; } for custom sorting.

cpp

std::sort(container.begin(), container.end(), std::greater<>());

Example

This example shows how to sort a vector of integers in descending order using std::greater<>(). It prints the vector before and after sorting.

cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional> // for std::greater

int main() {
    std::vector<int> numbers = {5, 2, 9, 1, 5, 6};

    std::cout << "Before sorting: ";
    for (int n : numbers) {
        std::cout << n << ' ';
    }
    std::cout << '\n';

    std::sort(numbers.begin(), numbers.end(), std::greater<>());

    std::cout << "After sorting (descending): ";
    for (int n : numbers) {
        std::cout << n << ' ';
    }
    std::cout << '\n';

    return 0;
}

Output

Before sorting: 5 2 9 1 5 6 
After sorting (descending): 9 6 5 5 2 1 

Common Pitfalls

Common mistakes when sorting in descending order include:

• Forgetting to include the comparator, which results in ascending order.
• Using std::less<>() or no comparator, which sorts ascending by default.
• Passing incorrect iterators or container types.

Always ensure the comparator matches the desired order.

cpp

#include <algorithm>
#include <vector>

// Wrong: sorts ascending (default)
// std::sort(vec.begin(), vec.end());

// Right: sorts descending
// std::sort(vec.begin(), vec.end(), std::greater<>());

Quick Reference

Usage	Description
std::sort(begin, end);	Sorts in ascending order by default
std::sort(begin, end, std::greater<>());	Sorts in descending order using built-in comparator
std::sort(begin, end, [](auto a, auto b) { return a > b; });	Sorts in descending order using lambda function

Key Takeaways

Use std::sort with std::greater<>() to sort in descending order easily.

Without a comparator, std::sort sorts in ascending order by default.

You can use a lambda function for custom descending order sorting.

Always pass valid iterators to std::sort to avoid runtime errors.

Include and headers when using std::sort and std::greater.