1、使用函数指针

#include <iostream>
#include <vector>
#include <algorithm> 
struct Person {
	std::string name;
	int age;
};

//自定义升序排序函数
bool Compare(const Person& a, const Person& b)
{
	return a.age < b.age;
}

int main() {
	// 创建一个包含多个Person对象的向量
	std::vector<Person> people = {{"Alice", 30}, {"Bob", 25}, {"Charlie", 35}};
	//排序
	std::sort(people.begin(), people.end(), Compare);
	// 输出排序后的结果
	for (const auto& person : people) {
		std::cout << person.name << ": " << person.age << std::endl;
	}
	return 0;
}

2、使用lambda表达式

#include <iostream>
#include <vector>
#include <algorithm> 
struct Person {
	std::string name;
	int age;
};

int main() {
	// 创建一个包含多个Person对象的向量
	std::vector<Person> people = {{"Alice", 30}, {"Bob", 25}, {"Charlie", 35}};
	//排序
	std::sort(people.begin(), people.end(), [](const Person& a, const Person& b){return a.age < b.age;});
	// 输出排序后的结果
	for (const auto& person : people) {
		std::cout << person.name << ": " << person.age << std::endl;
	}
	return 0;
}

3、使用仿函数(函数对象)

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

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

//仿函数(函数对象)
struct Comparest{
	bool operator()(const Person& a, const Person& b) const {
		return a.age < b.age;
	}
};

int main() {
	// 创建一个包含多个Person对象的向量
	std::vector<Person> people = {{"Alice", 30}, {"Bob", 25}, {"Charlie", 35}};
	//排序
	std::sort(people.begin(), people.end(), Comparest());
	// 输出排序后的结果
	for (const auto& person : people) {
		std::cout << person.name << ": " << person.age << std::endl;
	}
	return 0;
}

4、重载运算符

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

struct Person {
	std::string name;
	int age;
	//自定义升序排序算法(结构体内部重载)
	bool operator<(const Person& a) const
	{
		return age < a.age; //如果是age > a.age，则是降序排列
	}
};

////自定义升序排序算法(结构体外部重载)
//bool operator<(const Person& a, const Person& b)
//{
//	return a.age < b.age; //如果是a.age > b.age，则是降序排列
//}

int main() {
	// 创建一个包含多个Person对象的向量
	std::vector<Person> people = {{"Alice", 30}, {"Bob", 25}, {"Charlie", 35}};
	//排序,重载了运算符，不需要指定排序算法了
	std::sort(people.begin(), people.end());
	// 输出排序后的结果
	for (const auto& person : people) {
		std::cout << person.name << ": " << person.age << std::endl;
	}
	return 0;
}

map用结构体作为key的方法1，利用仿函数

#include <iostream>
#include <vector>
#include <algorithm> 
#include <map>
using namespace std;

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

//仿函数(函数对象)
struct Comparest{
	bool operator()(const Person& a, const Person& b) const {
		return a.age < b.age;
	}
};

int main() {
	// 创建一个包含多个Person对象的map
	std::map<Person, int, Comparest> peoplemap;
	peoplemap[{"Alice", 30}] = 0;
	peoplemap[{"Bob", 25}] = 1;
	peoplemap[{"Charlie", 35}] = 2;
	for(const auto& per:peoplemap){
		cout<<per.first.name<<" "<<per.first.age<<endl;
	}
	return 0;
}

map用结构体作为key的方法2，重载操作符

#include <iostream>
#include <vector>
#include <algorithm> 
#include <map>
using namespace std;

struct Person {
	std::string name;
	int age;
	bool operator<(const Person& a) const{
		return age < a.age;
	}
};

int main() {
	// 创建一个包含多个Person对象的map
	std::map<Person, int> peoplemap;
	peoplemap[{"Alice", 30}] = 0;
	peoplemap[{"Bob", 25}] = 1;
	peoplemap[{"Charlie", 35}] = 2;

	for(const auto& per:peoplemap){
		cout<<per.first.name<<" "<<per.first.age<<endl;
	}
	return 0;
}