Question

我正在做一些功课并收到最奇怪的错误。希望你能提供帮助。我收到了这个错误：

无法访问班级中的私人会员

注意：我显然没有写完这个，但我试着去测试错误。非常感谢您提供的任何意见！

// Amanda 
// SoccerPlayer.cpp : main project file.
// October 6, 2012
/* a. Design a SoccerPlayer class that includes three integer fields: a player's jersey     number,
number of goals, and number of assists. Overload extraction and insertion operators for     the class.
b. Include an operation>() function for the class. One SoccerPlayer is considered greater
than another if the sum of goals plus assists is greater.
c. Create an array of 11 SoccerPlayers, then use the > operator to find the player who   has the
greatest goals plus assists.*/

#include "stdafx.h"
#include<conio.h>
#include<iostream>
#include<string>



class SoccerPlayer
{
    friend std::ostream operator<<(std::ostream, SoccerPlayer&);
//  friend std::istream operator>>(std::istream, SoccerPlayer&);
private:
    int jerseyNum;
    int numGoals;
    int numAssists;
public:
    SoccerPlayer(int, int, int);

};

SoccerPlayer::SoccerPlayer(int jersey, int goal, int assist)
{
    jerseyNum = jersey;
    numGoals = goal;
    numAssists = assist;
} 

std::ostream operator<<(std::ostream player,  SoccerPlayer& aPlayer)
{
    player << "Jersey #" << aPlayer.jerseyNum <<
        " Number of Goals " << aPlayer.numGoals << 
        " Number of Assists " << aPlayer.numAssists;
    return player ;
};

int main()
{
return 0;
}

Answer 1

您希望通过引用传递和返回流：您无法复制IOStream对象。此外，在写入的情况下，您可能想要传递SoccerPlayer const&。通过这些更改，您的代码应该是编译器（尽管在定义输出运算符之后还有一个多余的分号）。

也就是说，输出运算符应声明为

std::ostream& operator<< (std::ostream&, SockerPlayer const&)

（在其定义和friend声明中）。

Answer 2

std::ostream不可复制。您需要传递引用，并返回引用：

friend std::ostream& operator<<(std::ostream&, const SoccerPlayer&);

....
std::ostream& operator<<(std::ostream& player,  const SoccerPlayer& aPlayer) { /* as before */ }

另请注意，没有理由不将SoccerPlayer作为const引用传递。

在与错误完全无关的注释上，您应该更喜欢使用构造函数初始化列表，而不是将值赋给构造函数体中的数据成员：

SoccerPlayer::SoccerPlayer(int jersey, int goal, int assist) 
: jerseyNum(jersey), numGoal(goal), numAssists(assist) {}

Answer 3

您应该将ostream对象的引用发送给您的朋友函数。所以它会像friend std::ostream& operator<<(std::ostream &, SoccerPlayer&); 无论是原型还是定义。

Answer 4

std::ostream operator<<(std::ostream player, SoccerPlayer& aPlayer)必须是班级的朋友或班级成员才能访问private和protected字段。

C ++重载提取运算符 - 错误无法访问类中声明的私有成员

4 个答案: