When sorting elements in C++, it is sometimes necessary to use custom sorting criteria, especially when working with user-defined data types. By default, the sorting order is determined by the comparison operators defined for the data type. However, there may be cases where the default sorting order is not suitable, and you need to define custom sorting literals to achieve the desired result.

In this blog post, we will discuss how to implement custom sorting literals in C++. We will use the std::sort function from the <algorithm> library to sort a vector of custom objects based on a specific criterion.

The Problem

Let’s imagine that we have a Person class with the following attributes:

class Person {
public:
    std::string name;
    int age;
};

Now, let’s say we have a vector of Person objects, and we want to sort them based on their age. By default, std::sort will use the default comparison operator (<) to determine the sorting order. However, in our case, we want to sort the Person objects in ascending order of their age.

Custom Sorting Literal

To achieve this, we need to define a custom sorting literal that compares Person objects based on their age. We can do this by overloading the less-than (<) operator for the Person class.

bool operator<(const Person& p1, const Person& p2) {
    return p1.age < p2.age;
}

Now, when the std::sort function is called on a vector of Person objects, it will use our custom < operator instead of the default one. This will ensure that the objects are sorted based on their age.

Here is an example of how to use the custom sorting literal with std::sort:

std::vector<Person> persons = {{"John", 25}, {"Alice", 30}, {"Bob", 20}};
std::sort(persons.begin(), persons.end());

// Output: Bob, John, Alice
for (const auto& person : persons) {
    std::cout << person.name << " ";
}

In the above code snippet, the persons vector is sorted using the custom sorting literal based on the age of the Person objects. The output is Bob, John, Alice, which is the expected sorting order based on their ages.

Conclusion

In C++, you can define custom sorting literals by overloading the comparison operators for your custom data types. This allows you to sort objects based on specific criteria instead of relying on the default comparison operators.

Custom sorting literals are especially useful when working with complex data structures or when the default sorting order is not suitable for your requirements. By implementing custom sorting literals, you have full control over how your objects are sorted.

Remember to always consider the performance implications of your custom sorting literals, as they can impact the overall sorting time.