String and+

Use + to string Object assignment is , Pay attention to the first + You must have one around string object , Otherwise, it will report a mistake

#include<iostream>
#include<string>
using namespace std;
int main()
{
    string s;
    //string s1 = s+"hello" + "hi"+s;
    string s2 = "hello" + "hi";
    string s3 = "hello" + "hi" +s;
    return 0;
}

linux Report a mistake

 vs Report a mistake

c++ primer  explain