Question

        // This program defines a person class which includes an
        // overloaded insertion operator.
        // Also included is a personDisplay manipulator
        // that displays a message and sets a field size
        // for the name

    #include<iostream>
    #include<fstream>
    #include<string>
    #include<iomanip>
        using namespace std;
    class Person
    {
    private:
        int idNum;
        string name;
    public:
        Person(const int, const string);
        friend ostream& operator<<(ostream&, const Person&);
    };
    Person::Person(int id, string nm)
    {
        idNum = id;
        name = nm;
    }
    ostream& operator<<(ostream& out, const Person& p)
    {
        out << p.name << " " << p.idNum << endl;
        return out;
    }
    ostream& personDisplay(ostream& out, Person& p)
    {

        out << "Here is a person: ";
        out.setf(ios::left);
        out.width(12);
        return out;
    }
    int main()
    {
        Person someBody(365, "Gabby");
        cout << personDisplay << someBody << endl;
        int dog;
        cin >> dog;
        return 0;
    }

This program is supposed to output "Here is a person:...". instead it outputs "002A11DI...". It does output "Gabby 365". Please help me find the source of the error. Thank you for your help.

Answer 1

呃我不知道从哪里开始。首先personDisplay不是运算符重载。要调用此函数，您应该使用：

personDisplay(std::cout, someBody);

第二

std::cout << personDisplay () << ...

由于personDisplay()返回out所在的引用（地址），因此将打印“垃圾”。（正如Igor Tandetnik在评论中所说）

您可以做的第三个也是唯一的选择是：

int main()                                                                                                                                    
{   
    Person someBody(365, "Gabby");
    personDisplay(std::cout, someBody) 
    cout << someBody << endl;
    int dog;
    cin >> dog;
    return 0;
}

C++ program has weird output

1 个答案: