string中单个字符存取方式有两种

代码如下：

#include <iostream>
using namespace std;
#include <cstring>//string 字符存取
void test01() {string str = "hello";cout << "str = " << str << endl;for (int i = 0; i < str.size(); i++) {cout << str[i];}cout << endl;for (int i = 0; i < str.size(); i++) {cout << str.at(i);}cout << endl;str[0] = 'x';cout << "str = " << str << endl;str.at(1) = 'x';cout << "str = " << str << endl;}int main() {test01();return 0;
}