How to correctly use the C++sort function to implement customized sorting function

The sort function uses a custom comparison function to implement customized sorting: write a comparison function: specify the sorting rules, define parameter types and return values. Call the sort function: pass the custom comparison function as the third parameter to sort the elements in the container. Example: Sort integers in descending order and strings according to custom rules (empty string first, length first, lexicographic order).

How to use the sort function in C to implement customized sorting function

sort function is an important function in the C standard library, used to sort The elements in the container are sorted. It receives a comparison function by reference, allowing the user to sort elements based on custom criteria.

The syntax of comparison function

The syntax of comparison function is as follows:

bool compare(const T1& a, const T2& b);

Among them:

• ##T1 and T2 are the element types to be compared.
Return
• true means a is less than b.
Return
• false means a is greater than or equal to b.

Implementing a custom sort

To implement a custom sort using the

sort function, you need to write a custom comparison function that specifies the sorting behavior . Here is an example:

#include <algorithm>
#include <vector>

using namespace std;

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

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

  sort(numbers.begin(), numbers.end(), compareIntsDescending);

  for (auto& num : numbers) {
    cout << num << " ";
  }
  cout << endl;

  return 0;
}

Output of this program:

5 4 3 2 1

In this example,

compareIntsDescending comparison function converts integers from large to small Sort.

Practical case: Sorting strings by custom rules

Suppose you have an array of strings and you want to sort them according to the following rules:

Empty strings are sorted first.
• Longer strings are sorted first (or in alphabetical order if the length is the same).

You can write the following comparison function to achieve this functionality:

bool compareStrings(string a, string b) {
  // 检查是否为空字符串
  if (a.empty() && !b.empty()) {
    return true;
  } else if (!a.empty() && b.empty()) {
    return false;
  }

  // 空字符串相等
  if (a.empty() && b.empty()) {
    return false;
  }

  // 比较长度
  if (a.length() < b.length()) {
    return true;
  } else if (a.length() > b.length()) {
    return false;
  }

  // 长度相同时按字母顺序比较
  return (a < b);
}

You can then use this comparison function to sort the string array as follows:

#include <algorithm>
#include <vector>

using namespace std;

int main() {
  vector<string> strings = {"apple", "banana", "cherry", "dog", "cat", ""};

  sort(strings.begin(), strings.end(), compareStrings);

  for (auto& str : strings) {
    cout << str << " ";
  }
  cout << endl;

  return 0;
}

Output of this program:

 dog cat apple banana cherry

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