you must have lost a little bit. You haven't defined the operation istream on the left, Person on the right, and in the middle.

cPP primer?

@ 7856 is right. First of all, there is no original answer book, it is written by the translator himself, and there are some mistakes, so sometimes you can't believe all the answers.

if you take a closer look at the example of Sales_data in Primer, there is no definition of the operator is > > * this . If you want to write in this way, you have to provide the definition of . And the second public keyword in the answer is obviously superfluous.

it should be written like this:

-sharppragma once
-sharpinclude <iostream>
-sharpinclude <string>
class Person{

friend std::istream &read(std::istream &is, Person &per);
public:
    Person() = default;
    Person(const std::string &name, const std::string &add)
    {
        strName = name;
        strAddress = add;
    }
    Person(std::istream &is) { read(is, *this); }

    std::string getName() const { return strName; }
    std::string getAddress() const { return strAddress; }

private:
    std::string strName;
    std::string strAddress;

};

std::istream &read(std::istream &is, Person &per)
{
    is >> per.strName >> per.strAddress;
    return is;
}
std::ostream &print(std::ostream &os, const Person &per)
{
    os << per.getName() << per.getAddress();
    return os;
}

• read and print are not member functions, they are just functions related to this class, so don't put them inside class, just put them outside
.
• in fact, you must put this class in a header file. Do not use using namespace std in the header file. There is no using namespace std; . When you write function parameters, you should also write as std::string .