replace()用法

#include<iostream>
#include<string>
using namespace std;
int main()
{string str = "abcdef";str.replace(0,3,"XXX");cout << str << endl;       //输出: XXXdefstr.replace(0, 3, 3, 'Y');cout << str << endl;	   //输出: YYYdefstring s = "2020";str.replace(0, 3, s, 0, 3);cout << str << endl;       //输出: 202defreturn 0;
}