STL resize capacity rule set

1、

#include <iostream>
#include<vector>
#include<list>
using namespace std;

void fun1()
{
    string db(5, 'a');
    cout << db.capacity() << endl;
    db.resize(3);// law ： Reset the number of elements , If the number of elements is less than the default capacity （ Default capacity is 15, Reset the number of elements to 3）, Then the capacity remains the same ; If the number of reset elements is greater than the capacity, the capacity will increase , If the set capacity is 6, If the number of elements is reset to 17, Then the capacity is 31.
    cout << db << endl;
    cout << db.capacity() << endl;
    db.resize(17);//15 31 47 Regular increase :15 16 16
    cout << db.capacity() << endl;

    vector<int> db2(6);
    cout << db2.capacity() << endl;
    db2.resize(3);// Reset the number of elements , Equal to capacity （ For example, set the capacity to 6, Reset the number of elements to 3）, Then the capacity remains the same ; If the number of reset elements is greater than the capacity, the capacity will increase , If the set capacity is 6, If the number of elements is reset to 7, Then the capacity is 6+6/2=9.
    cout << db2.capacity() << endl;
    db2.resize(7); 
    cout << db2.capacity() << endl;
    
    list<int> db3(5);
    cout << db3.size() << endl;
    db3.resize(3);// Reset the number of elements , Capacity （ For example, set the capacity to 5, Reset the number of elements to 3）, Then the capacity is 3.
    cout << db3.size() << endl;
    db3.resize(7);
    cout << db3.size() << endl;

    
}
int main()
{
    fun1();
    system("pause");
    return 0;
}