如何使用头文件中预定义的Friend方法？

debugcn 发表于 Dev

罗汉·帕里克（Rohan Parikh）

本质上，我的计算机科学老师让我使用朋友std :: ostream方法进行输出。如下所示，我已将其导入头文件中，但是我不知道如何在student.cpp中使用它。添加Student :: ostream无效。我将如何在student.cpp中使用标头预定义方法

我的头文件

#pragma once
#include <iostream>
class student
{
public:
    student();
    std::string settingStudentName;
    bool disiplineIssue();

    // provided again so you learn this valuable override method for printing class data.
    friend std::ostream& operator << (std::ostream& const student &);

private:
    std::string studentName;
    bool hasDisciplineIssue;
};

学生.cpp

#include "student.h"
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

student::student()
{
    
}


bool student::disiplineIssue()
{
    // Max the random integer can go
   int max = 100;
   srand(time(0));
   int random = rand()%max;

    // bool variable for returning
    bool True_or_False = false;
   if (random <= 5)
   {
       True_or_False = true;
   }
   return True_or_False;    
}

ostream& operator<< (ostream& output, const student& aStudent) {
    
    output << aStudent.studentName << " ";
    if (aStudent.hasDisciplineIssue) {
        output << "has ";
    }
    else {
        output << "doesn't have ";
    }
    output << "a discipline issue";
    return output;
}

编辑：当我前面没有student ::时，ostream可以工作，但是如果我在前面添加student :::它表示无法解析该符号。我不确定没有学生的那一个::是否正在使用我在头文件中定义的那个。

林戈

我将以以下方式进行：

添加主体和声明参数以settingStudentName在头文件和主文件中起作用；
插入正确的依存关系（#include）;
添加main()驱动程序功能；
同样，使用正确的语法（friend std::ostream& operator << (std::ostream&, const student &);）缺少,函数参数之间的逗号分隔符。

MWE：

#ifndef STUDENT_H_INCLUDED
#define STUDENT_H_INCLUDED

#include <iostream>
#include <string>
class student
{
public:
    student();
    std::string settingStudentName(const std::string&);
    bool disiplineIssue();

    // provided again so you learn this valuable override method for printing class data.
    friend std::ostream& operator << (std::ostream&, const student &);

private:
    std::string studentName;
    bool hasDisciplineIssue;
};

#endif // STUDENT_H_INCLUDED

#include "student.h"
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <string>

using namespace std;

student::student()
{

}

string student::settingStudentName(const string& input)
{
    studentName = input;

    return input;
}

bool student::disiplineIssue()
{
    // Max the random integer can go
   int max = 100;
   srand(time(0));
   int random = rand()%max;

    // bool variable for returning
    bool True_or_False = false;
   if (random <= 5)
   {
       True_or_False = true;
   }
   return True_or_False;
}

ostream& operator<< (ostream& output, const student& aStudent) {

    output << aStudent.studentName << " ";
    if (aStudent.hasDisciplineIssue) {
        output << "has ";
    }
    else {
        output << "doesn't have ";
    }
    output << "a discipline issue";
    return output;
}


int main()
{
    student Jack;
    Jack.settingStudentName("Jack");
    Jack.disiplineIssue();

    cout << Jack << endl;

    return 0;
}

这是输出：