C++ std::sort Explained: How to Sort Vectors and Arrays for Beginners

Sorting is one of the most common operations in programming — arranging a list of names alphabetically, ordering scores from highest to lowest, or ranking items by price. C++ gives you std::sort from the <algorithm> header, and it’s both fast (O(n log n)) and easy to use.

Sorting a Vector: The Basics

Include <algorithm> and pass iterators pointing to the beginning and end of your container:

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {5, 2, 8, 1, 9, 3};

    std::sort(nums.begin(), nums.end());

    for (int n : nums) {
        std::cout << n << " ";
    }
    // Output: 1 2 3 5 8 9
    return 0;
}

nums.begin() points to the first element; nums.end() points one past the last. This two-iterator pattern is used throughout the entire C++ standard library.

Sorting in Descending Order

Pass std::greater<T>() as a third argument:

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>

int main() {
    std::vector<int> nums = {5, 2, 8, 1, 9, 3};

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

    for (int n : nums) {
        std::cout << n << " ";
    }
    // Output: 9 8 5 3 2 1
    return 0;
}

The third argument is a comparator — a function (or object) that tells sort which element should come first. std::greater<int>() says “larger values come first.”

Sorting Strings

std::sort works just as well on strings — alphabetically by default:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

int main() {
    std::vector<std::string> names = {"Charlie", "Alice", "Bob", "Diana"};

    std::sort(names.begin(), names.end());

    for (const auto& name : names) {
        std::cout << name << "\n";
    }
    // Alice, Bob, Charlie, Diana
    return 0;
}

Sorting a Portion of a Vector

You don’t have to sort the whole container. Use pointer arithmetic to sort just a slice:

std::vector<int> v = {9, 3, 7, 1, 5, 2, 8};

// Sort only the first 4 elements
std::sort(v.begin(), v.begin() + 4);

for (int n : v) std::cout << n << " ";
// Output: 1 3 7 9 5 2 8

Custom Comparators with Lambdas

The real power of std::sort is the custom comparator. Use a lambda function to define any ordering you want:

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {5, 2, 8, 1, 9, 3};

    // Sort by absolute distance from 5
    std::sort(nums.begin(), nums.end(), [](int a, int b) {
        return std::abs(a - 5) < std::abs(b - 5);
    });

    for (int n : nums) std::cout << n << " ";
    // 5 3 8 2 9 1  (closest to 5 first)
    return 0;
}

The lambda takes two elements and returns true if the first should come before the second.

Sorting Custom Objects

Here’s a practical example: sorting a list of students by score, then alphabetically for ties:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

struct Student {
    std::string name;
    int score;
};

int main() {
    std::vector<Student> students = {
        {"Charlie", 85},
        {"Alice", 92},
        {"Bob", 85},
        {"Diana", 78}
    };

    // Sort by score descending, then name ascending on tie
    std::sort(students.begin(), students.end(), [](const Student& a, const Student& b) {
        if (a.score != b.score) return a.score > b.score;
        return a.name < b.name;
    });

    for (const auto& s : students) {
        std::cout << s.name << ": " << s.score << "\n";
    }
    return 0;
}

Output:

Alice: 92
Bob: 85
Charlie: 85
Diana: 78

Bob comes before Charlie because their scores tie at 85 and “Bob” < “Charlie” alphabetically.

Sorting Arrays (Not Just Vectors)

std::sort works on raw arrays too using pointer syntax:

#include <algorithm>
#include <iostream>

int main() {
    int arr[] = {4, 1, 7, 2, 5};
    int size = 5;

    std::sort(arr, arr + size);

    for (int i = 0; i < size; i++) std::cout << arr[i] << " ";
    // 1 2 4 5 7
    return 0;
}

Related Articles

• C++ Vector Tutorial: The Complete Guide to std::vector
• C++ Lambda Functions Explained: Closures, Captures, and std::function
• C++ STL Containers Explained: Choosing the Right Container
• Merge Sort in C++: How It Works and How to Implement It

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