Custom sorting literals in C++

23 Oct 2023

References

Sorting is a fundamental operation in programming that allows us to arrange elements in a specific order. By default, most programming languages have built-in sorting functions that work well for a wide range of scenarios. However, there may be cases where we need to sort elements in a custom order that is not supported by the default sorting algorithm.

In this blog post, we will explore how to implement custom sorting literals in C++. Custom sorting literals allow us to define our own rules for sorting elements based on specific criteria, providing us with more flexibility and control over the sorting process.

Understanding Sorting in C++

In C++, sorting is typically performed using the std::sort function from the <algorithm> header. The std::sort function sorts elements in ascending order by default, but it can also be customized to sort in descending order or based on a custom sorting function.

For example, consider an array of integers that we want to sort in descending order:

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

bool compare(int a, int b) {
  return a > b;
}

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

  std::sort(numbers.begin(), numbers.end(), compare);

  for (int number : numbers) {
    std::cout << number << " ";
  }

  return 0;
}

In this code snippet, we define a custom comparison function compare that sorts integers in descending order. We pass this function as the third argument to std::sort to customize the sorting order.

Implementing Custom Sorting Literals

To implement custom sorting literals in C++, we can define a custom class or struct that overloads the less-than (<) operator. This allows us to define the custom sorting rules based on the desired criteria.

Let’s consider a scenario where we have a collection of objects representing students. We want to sort the students based on their names, but we want the sorting to be case-insensitive. Here’s how we can implement this custom sorting literal:

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

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

bool operator<(const Student& lhs, const Student& rhs) {
  std::string name1 = lhs.name;
  std::string name2 = rhs.name;

  // Convert names to lowercase for case-insensitive comparison
  std::transform(name1.begin(), name1.end(), name1.begin(), ::tolower);
  std::transform(name2.begin(), name2.end(), name2.begin(), ::tolower);

  return name1 < name2;
}

int main() {
  std::vector<Student> students = {
      {"Alice", 20},
      {"bob", 19},
      {"Charles", 21},
      {"david", 18},
  };

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

  for (const Student& student : students) {
    std::cout << student.name << " (age: " << student.age << ")" << std::endl;
  }

  return 0;
}

In this code snippet, we define a custom operator< in the Student struct. This operator converts the names to lowercase before performing the comparison. By overloading the < operator, we specify that the objects should be sorted based on their names with case-insensitive comparison.

Conclusion

Custom sorting literals provide us with the ability to define our own rules for sorting elements based on specific criteria. In C++, we can implement custom sorting literals by overloading the less-than (<) operator in a custom class or struct. This allows us to customize the sorting process, enabling us to meet our specific requirements.

By customizing the sorting process, we can sort elements in a way that is not supported by the default sorting algorithms, which gives us greater control and flexibility in our programs.

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