c++ sort string

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11-03-2025

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Sorting strings in C++ is a common task with several approaches. This guide explores various methods, from using standard library functions to implementing custom comparison functions for nuanced sorting needs. We'll cover the basics and delve into more advanced scenarios.

Using std::sort for Basic String Sorting

The simplest way to sort strings in C++ is using the std::sort algorithm from the <algorithm> header. std::sort utilizes an efficient sorting algorithm (typically IntroSort, a hybrid of quicksort, heapsort, and insertion sort) to rearrange elements in a given range.

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

int main() {
  std::vector<std::string> strings = {"banana", "apple", "orange", "grape"};

  std::sort(strings.begin(), strings.end()); //Sorts in lexicographical order

  for (const std::string& str : strings) {
    std::cout << str << " ";
  }
  std::cout << std::endl; // Output: apple banana grape orange

  return 0;
}

This code snippet sorts the strings vector in lexicographical (dictionary) order. This is the default behavior of std::sort when comparing strings.

Sorting in Reverse Order

To sort strings in reverse lexicographical order, you can use a custom comparison function with std::sort.

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

bool compareReverse(const std::string& a, const std::string& b) {
  return a > b; // Reverse lexicographical comparison
}

int main() {
  std::vector<std::string> strings = {"banana", "apple", "orange", "grape"};
  std::sort(strings.begin(), strings.end(), compareReverse);

  for (const std::string& str : strings) {
    std::cout << str << " ";
  }
  std::cout << std::endl; // Output: orange grape banana apple

  return 0;
}

Here, compareReverse defines the comparison logic, resulting in a reversed sorted order.

Case-Insensitive String Sorting

Lexicographical sorting is case-sensitive. To perform a case-insensitive sort, you need a custom comparison function that ignores case differences.

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <cctype> //For tolower

bool compareIgnoreCase(const std::string& a, const std::string& b) {
  std::string lowerA = a;
  std::string lowerB = b;
  std::transform(lowerA.begin(), lowerA.end(), lowerA.begin(), ::tolower);
  std::transform(lowerB.begin(), lowerB.end(), lowerB.begin(), ::tolower);
  return lowerA < lowerB;
}

int main() {
  std::vector<std::string> strings = {"Banana", "apple", "Orange", "grape"};
  std::sort(strings.begin(), strings.end(), compareIgnoreCase);

  for (const std::string& str : strings) {
    std::cout << str << " ";
  }
  std::cout << std::endl; // Output: apple Banana grape Orange

  return 0;
}

This example uses std::transform and ::tolower to convert strings to lowercase before comparison, achieving case-insensitive sorting.

Sorting Strings by Length

You can sort strings based on their lengths by defining a comparison function that checks string lengths.

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

bool compareByLength(const std::string& a, const std::string& b) {
  return a.length() < b.length();
}

int main() {
  std::vector<std::string> strings = {"apple", "kiwi", "banana", "grape"};
  std::sort(strings.begin(), strings.end(), compareByLength);

  for (const std::string& str : strings) {
    std::cout << str << " ";
  }
  std::cout << std::endl; // Output: kiwi grape apple banana

  return 0;
}

This code sorts strings from shortest to longest. Modifying the comparison to return a.length() > b.length(); would reverse the order.

Sorting Strings using std::stable_sort

std::stable_sort maintains the relative order of equal elements. If you need to preserve the original order of strings with the same lexicographical value, use std::stable_sort.

Conclusion

C++ offers flexible ways to sort strings, from simple lexicographical ordering to more complex scenarios requiring custom comparison functions. Understanding these techniques empowers you to efficiently manage and manipulate string data in your C++ programs. Remember to choose the method that best suits your specific sorting requirements. The use of std::sort with appropriate comparison functions provides a powerful and efficient solution for various string sorting tasks.