Custom sorting literals in C++

23 Oct 2023

References

Sorting is a common operation in programming, but what if you need to sort elements in a specific order that is not default? In C++, you can achieve this by using custom sorting literals.

Sorting with Custom Comparison Function

The std::sort function in C++ uses a comparison function to determine the order of elements. By default, it uses the less than (<) operator to compare elements. However, you can provide a custom comparison function to define your own sorting criteria.

Let’s say we have a Person class with name and age attributes. We want to sort a vector of Person objects based on their name in alphabetical order. Here’s how we can do it:

struct Person {
    std::string name;
    int age;
};

// Custom comparison function
bool compareByName(const Person& p1, const Person& p2) {
    return p1.name < p2.name;
}

int main() {
    std::vector<Person> people = {
        {"Alice", 25},
        {"Bob", 30},
        {"Charlie", 20}
    };

    std::sort(people.begin(), people.end(), compareByName);

    for (const Person& person : people) {
        std::cout << person.name << " - Age: " << person.age << std::endl;
    }

    return 0;
}

In this example, we define the compareByName function as the custom comparison function. It compares two Person objects based on their name attributes using the less than operator. We then pass this function as the third argument to the std::sort function.

Running this code will output the sorted list of people based on their names:

Alice - Age: 25
Bob - Age: 30
Charlie - Age: 20

Sorting with Lambda Functions

C++11 introduced lambda functions, which are anonymous functions that can be used inline. They are particularly useful when you want to define a custom comparison function without declaring a separate function.

Using the previous example, we can rewrite the code using a lambda function:

int main() {
    std::vector<Person> people = {
        {"Alice", 25},
        {"Bob", 30},
        {"Charlie", 20}
    };

    std::sort(people.begin(), people.end(), [](const Person& p1, const Person& p2) {
        return p1.name < p2.name;
    });

    for (const Person& person : people) {
        std::cout << person.name << " - Age: " << person.age << std::endl;
    }

    return 0;
}

The lambda function [](const Person& p1, const Person& p2) takes two Person objects as parameters and compares them based on their name attributes. This inline function is directly passed as the third argument to std::sort.

Conclusion

Custom sorting literals in C++ allow you to sort elements in a specific order that is not default. By providing a custom comparison function or using lambda functions, you can define your own sorting criteria. This flexibility makes it easier to handle various sorting requirements in your C++ programs.

#References