4

我很难重载 << 运算符。我正在做一个家庭作业，我只能修改代码的某些部分。在你问之前，我坚持使用结构而不是类。以下是受影响代码的部分：

调用函数是：

/*
 * Write a CSV report listing each course and its enrollment.
 */
void generateReport (ostream& reportFile,
             int numCourses,
             Course* courses)
{
  for (int i = 0; i < numCourses; ++i)
    {
        //courses is an array of "Course" structs
        reportFile << courses[i] << endl;
    }
}

这是.h文件：

#ifndef COURSE_H
#define COURSE_H

#include <iostream>
#include <string>


struct Course {
    std::string name;
    int maxEnrollment;
    int enrollment;

    Course();
    Course(std::string cName);

    std::ostream& operator << (ostream &out, const Course &c);
};

#endif

这是 .cpp 文件：

#include "course.h"

using namespace std;


Course::Course()
{
    name = "";
    maxEnrollment = 0;
    enrollment = 0;
}

Course::Course(string cName)
{
    name = cName;
    maxEnrollment = 0;
    enrollment = 0;
}

// send course to file
ostream& Course::operator << (ostream &out, const Course &c)
{
    out << c.name << "," << c.enrollment << endl;
    return out;
}

这是我不断收到的错误消息：

错误：将 'operator<<' 声明为非函数|

我已经在互联网上搜索了几个小时，并尝试了很多不同的方法来解决这个问题，但都没有成功。请帮忙！！

我根据建议尝试了几种不同的方法来解决这个问题。以下是我尝试过的两种方法，但均无效： 方法 1：

#ifndef COURSE_H
#define COURSE_H

#include <iostream>
#include <string>


struct Course {
    std::string name;
    int maxEnrollment;
    int enrollment;

    Course();
    Course(std::string cName);

};

//Moved this outside the struct
std::ostream& operator << (ostream &out, const Course &c);

#endif

方法二（也改失败错误）：

#include "course.h"

using namespace std;


Course::Course()
{
    name = "";
    maxEnrollment = 0;
    enrollment = 0;
}

Course::Course(string cName)
{
    name = cName;
    maxEnrollment = 0;
    enrollment = 0;
}

std::ostream& operator << (ostream &out, const Course &c);


// send course to file
ostream& Course::operator << (ostream &out, const Course &c)
{
    out << c.name << "," << c.enrollment << endl;
    return out;
}

重新编辑----------------------------------- --------- 经过一些评论和帮助，这是我当前的代码：

在 .h 文件中：

#ifndef COURSE_H
#define COURSE_H

#include <iostream>
#include <string>


struct Course {
    std::string name;
    int maxEnrollment;
    int enrollment;

    Course();
    Course(std::string cName);

    std::ostream& operator << (std::ostream &out, const Course &c);
};

#endif

在 .cpp 文件中：

#include "course.h"

using namespace std;

Course::Course()
{
    name = "";
    maxEnrollment = 0;
    enrollment = 0;
}

Course::Course(string cName)
{
    name = cName;
    maxEnrollment = 0;
    enrollment = 0;
}


// send course to file
ostream& operator << (ostream &out, const Course &c)
{
    out << c.name << "," << c.enrollment << endl;
    return out;
}
4

3 回答 3

8

您忘记在参数中包含<ostream>和命名空间说明符std::，这会导致您的错误。

如果您想了解下一个错误，请继续阅读：

std::ostream& operator << (std::ostream &out, const Course &c);

这意味着您定义了一个运算符，该运算符应该在Course左侧 ( *this) 的当前实例上工作，因为它被定义为成员。这将导致运算符具有一个左侧和两个右侧，这是不可能的。

您需要将运算符定义为非成员函数，因为左侧应该是 anostream&而不是Course&。

于 2013-03-31T20:16:28.107 回答
3 
std::ostream& operator << (std::ostream &out, const Course &c);

应该

friend std::ostream& operator << (std::ostream &out, const Course &c);

和

std::ostream& Course::operator << (std::ostream &out, const Course &c)   // Not a member of Course
{

应该

std::ostream& operator << (std::ostream &out, const Course &c)
{

由于它不是Course.

于 2013-03-31T20:15:04.580 回答
1

std::ostream& operator << (ostream &out, const Course &c);在Course声明中，必须声明为friend，否则不能带两个参数。

另外，第一个参数必须是std::ostream&而不仅仅是ostream&

于 2013-03-31T20:17:11.720 回答