学步园

1.

#include <iostream>
#include <string>
using namespace std;
 
class A
{
    public:
        A(string x)
        {
            test = x;
        }
        const char& operator[](size_t pos) const
        {return test[pos];}
        char& operator[](size_t pos)
        {return test[++pos];}
    private:
        string test;
};
int main()
{
    A a("Hello");
    cout << a[0];
    const A b("Hello");
    cout << b[0];
    return 0;
}

为什么const char& operator[](size_t pos) const 要返回一个const char &？