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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