c++ - 运算符重载 C++；<< 操作的参数太多

Question

我在下面有一些代码，它们会使用一些名字和年龄，并用它们做一些事情。最终它将打印出来。我需要print()用全局更改我的功能operator<<。我在另一个论坛上看到<<operator有两个参数，但是当我尝试它时，我得到一个“<< 操作错误的参数太多。我做错了什么吗？我是 C++ 新手，我真的不明白这一点运算符重载。

#include <iostream>;
#include <string>;
#include <vector>;
#include <string.h>;
#include <fstream>;
#include <algorithm>;

using namespace::std;

class Name_Pairs{
    vector<string> names;
    vector<double> ages;

public:
    void read_Names(/*string file*/){
        ifstream stream;
        string name;

        //Open new file
        stream.open("names.txt");
        //Read file
        while(getline(stream, name)){   
            //Push
            names.push_back(name);
        }
        //Close
        stream.close();
    }

    void read_Ages(){
        double age;
        //Prompt user for each age
        for(int x = 0; x < names.size(); x++)
        {
            cout << "How old is " + names[x] + "?  ";
            cin >> age;
            cout<<endl;
            //Push
            ages.push_back(age);
        }

    }

    bool sortNames(){
        int size = names.size();
        string tName;
        //Somethine went wrong
        if(size < 1) return false;
        //Temp
        vector<string> temp = names;
        vector<double> tempA = ages;
        //Sort Names
        sort(names.begin(), names.end());

        //High on performance, but ok for small amounts of data
        for (int x = 0; x < size; x++){
            tName = names[x];
            for (int y = 0; y < size; y++){
                //If the names are the same, then swap
                if (temp[y] == names[x]){
                    ages[x] = tempA[y];
                }
            }
        }
    }

    void print(){
        for(int x = 0; x < names.size(); x++){
            cout << names[x] << " " << ages[x] << endl;
        }
    }

    ostream& operator<<(ostream& out, int x){
        return out << names[x] << " " << ages[x] <<endl;
    }
};

Answer 1

您将<<运算符重载为成员函数，因此，第一个参数隐式地是调用对象。

您应该将其作为friend函数或自由函数重载。例如：

friend作为函数重载。

friend ostream& operator<<(ostream& out, int x){
     out << names[x] << " " << ages[x] <<endl;
     return out;
}

但是，规范的方法是将其作为free函数重载。您可以从这篇文章中找到非常好的信息：C++ 运算符重载

Answer 2

将运算符重载函数声明为友元。

friend ostream& operator<<(ostream& out, int x)
{
        out << names[x] << " " << ages[x] <<endl;
        return out;
}