How to sort C++ STL containers?

How to sort STL containers in C++: Use the sort() function to sort containers in place, such as std::vector. With ordered containers std::set and std::map, elements are automatically sorted on insertion. For a custom sort order, you can use a custom comparator class, such as sorting a vector of strings alphabetically.

How to sort C++ STL containers

STL (Standard Template Library) provides a series of flexible and efficient general algorithms for various types of containers operations, including sorting. The following sections describe several common ways to sort STL containers in C++.

Use the sort() function

std::sort() The function is the simplest function in C++ for container sorting. It accepts a reference or pointer to a container as input and sorts its elements in place. The following example demonstrates how to use the sort() function to sort a std::vector:

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

int main() {
  std::vector<int> v = {3, 1, 4, 2, 5};

  // 使用 sort() 函数对向量进行排序
  std::sort(v.begin(), v.end());

  // 打印排序后的向量
  for (int num : v) {
    std::cout << num << " ";
  }
  
  return 0;
}

Output:

1 2 3 4 5

Use the built-in sorting of std::set and std::map

std::set and std::map are ordered containers in C++ , they maintain their own collection of elements and automatically sort elements upon insertion. The following example shows how to use std::set to create and sort a set of integers:

#include <iostream>
#include <set>

int main() {
  std::set<int> s = {3, 1, 4, 2, 5};

  // 由于 std::set 是有序的，元素按升序存储
  for (int num : s) {
    std::cout << num << " ";
  }
  
  return 0;
}

Output:

1 2 3 4 5

Custom sorting comparator

If you need to customize the sorting order, you can implement it through a custom comparator class. The following example shows how to create a custom comparator that sorts a vector of strings alphabetically:

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

class StringComparator {
public:
  bool operator()(const std::string& a, const std::string& b) const {
    return a < b;
  }
};

int main() {
  std::vector<std::string> v = {"apple", "banana", "cherry", "dog", "elephant"};

  // 使用自定义比较器对向量进行排序
  std::sort(v.begin(), v.end(), StringComparator());

  // 打印排序后的向量
  for (const std::string& s : v) {
    std::cout << s << " ";
  }
  
  return 0;
}

Output:

apple banana cherry dog elephant

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