STLset container sorting

STLset container sorting

learning target:

The default sorting rule of set container is from small to large, master how to change the sorting rule

Main technical points:

Using functors, you can change the sorting rules

Code example one:

#include<iostream>
#include<set>
using namespace std;
//set容器排序
class Mycompare
{
    
    
public:
       bool operator()(int v1, int v2)
       {
    
    
              return v1 > v2;
       }
};
void test01()
{
    
    
       set<int>s1;
       s1.insert(10);
       s1.insert(40);
       s1.insert(50);
       s1.insert(30);
       s1.insert(20);
       for (set<int>::iterator it = s1.begin(); it != s1.end(); it++)
       {
    
    
              cout << *it << " ";
       }
     cout << endl;
       //指定排序规则为从小到大
       set<int, Mycompare>s2;
       s2.insert(10);
       s2.insert(40);
       s2.insert(50);
       s2.insert(30);
       s2.insert(20);
       for (set<int, Mycompare>::iterator it = s2.begin(); it != s2.end(); it++)
       {
    
    
              cout << *it << " ";
       }
       cout << endl;
}
int main()
{
    
    
       test01();
       system("pause");
       return 0;
}  

Summary: Use functors to specify the sorting rules of set containers

Code example two:

#include<iostream>
#include <string>
#include<set>
using namespace std;
//set容器排序,存放自定义数据类型
class Person
{
    
    
public:
       Person(string name, int age)
       {
    
    
              this->m_Name = name;
              this->m_age = age;
       }
       string m_Name;
       int m_age;
};
class comPerson
{
    
    
public:
class comPerson
{
    
    
public:
       bool operator()(const Person&p1, const Person&p2)
       {
    
    
              //按照年龄 降序
              return p1.m_age > p2.m_age;
       }
};
void test01()
{
    
    
       //自定义数据类型，都会指定排序规则
       set<Person, comPerson>s;
       //创建对象
       Person p1("刘备", 24);
       Person p2("关羽", 34);
       Person p3("张飞", 44);
       Person p4("赵云", 54);
       s.insert(p1);
       s.insert(p2);
       s.insert(p3);
       s.insert(p4);
       for (set<Person>::iterator it = s.begin(); it != s.end(); it++)
       {
    
    
              cout << "姓名：" << it->m_Name
                     << " 年龄：" << it->m_age << endl;
       }
       
}
int main()
{
    
    
       test01();
       system("pause");
       return 0;
}

Summary:
For custom data types, set must specify the sorting rules to insert data