重载

I've looked up information for overloading the << operator, and it seems like I did everything correctly, but I keep getting a compile error. I've friended this function in my header file, and placed a prototype at the top of my cpp file.

我查找了重载< <运算符的信息,似乎我做的一切都正确,但我一直得到编译错误。我已经在我的头文件中浏览了这个函数,并在我的cpp文件的顶部放置了一个原型。< p>

My University.h:

#ifndef UNIVERSITY_H
#define UNIVERSITY_H

#include <string>
#include <vector>
#include <iostream>

using namespace std;

#include "Department.h"
#include "Student.h"
#include "Course.h"
#include "Faculty.h"
#include "Person.h"


class University
{
  friend ostream& operator<< (ostream& os, const vector<Department>& D);
  friend ostream& operator<< (ostream& os, const Department& department);

 protected:
  vector<Department> Departments;
  vector<Student> Students;
  vector<Course> Courses;
  vector<Faculty> Faculties;
  static bool failure;
  static bool success;


 public:

  bool CreateNewDepartment(string dName, string dLocation, long dChairID);
  bool ValidFaculty(long dChairID);
};

#endif

My University.cpp:

#ifndef UNIVERSITY_CPP
#define UNIVERSITY_CPP

#include<string>
#include<vector>
#include<iostream>
using namespace std;

#include "University.h"

ostream& operator<<(ostream& os, const vector<Department>& D);
ostream& operator<<(ostream& os, const Department& department);

bool University::failure = false;
bool University::success = true;


bool University::CreateNewDepartment(string dName, string dLocation, long dChairID)
{
  if((dChairID != 0) && (ValidFaculty(dChairID)== University::failure))
    {
      Department D(dName, dLocation, dChairID);
      Departments.push_back(D);
      for (int i = 0; i < Departments.size(); i++)
         cout << Departments;
      return University::success;
    }
  return University::failure;
}

bool University::ValidFaculty(long dChairID)
{
  for (int i = 0; i < Faculties.size(); i++)
    {
      if (Faculties[i].ID == dChairID)
        return University::success;
    }
  return University::failure;
}

ostream& operator<<(ostream& os, const vector<Department>& D)
{
  for (int i = 0; i < D.size(); i++)
     os << D[i] << endl;
  os << "\n";
  return os;
}

ostream& operator<< (ostream& os, const Department& department)
{
    department.Print(os);
    return os;
}

#endif

My Department.h:

#ifndef DEPARTMENT_H
#define DEPARTMENT_H

#include<vector>
#include<string>
#include<iostream>
using namespace std;

class Department
{
  friend class University;
  friend ostream& operator<< (ostream& os, Department& department);

 protected:
  long ID;
  string name;
  string location;
  long chairID;
  static long nextDepartID;

 public:
  Department();
  Department(string dName, string dLocation, long dChairID);
  void Get();
  void Print(ostream& os)const;
};

#endif

My Department.cpp:

#ifndef DEPARTMENT_CPP
#define DEPARTMENT_CPP

#include<iostream>
#include<string>
using namespace std;

#include "Department.h"

long Department::nextDepartID = 100;

Department::Department()
{
  ID = nextDepartID++;
  name = "Null";
  location = "Null";
  chairID = 0;
}

Department::Department(string dName, string dLocation, long dChairID):name(dName), location(dLocation), chairID(dChairID)
{
  ID = nextDepartID++;
}

void Department::Get()
{
}

void Department::Print(ostream& os)const
{
  os << "\n";
  os << ID << endl;
  os << name << endl;
  os << location << endl;
  os << chairID << endl;
  os <<"\n\n";
}

ostream& operator<< (ostream& os, const Department& department)
{
  department.Print(os);
  return os;
}
#endif

Now everything can be seen that pertains only to this problem. The only error I receive now is that void value is not being ignored.

现在可以看到一切只与这个问题有关。我现在收到的唯一错误是不会忽略void值。

Snippet of error:

错误片段:

University.cpp: In function ‘std::ostream& operator<<(std::ostream&, const Department&)’:
University.cpp:53: error: void value not ignored as it ought to be
Department.cpp: In function ‘std::ostream& operator<<(std::ostream&, const Department&)’:
Department.cpp:42: error: void value not ignored as it ought to be

FINAL EDIT:

Thanks to everyone that helped me. I definitely have a better understanding of operator overloading now...especially when it deals with printing vectors of user-defined types!

感谢所有帮助过我的人。我现在肯定对运算符重载有了更好的理解......尤其是当它处理用户定义类型的打印向量时!

1 个解决方案

#1

The complaint was that while your function to iterate over and print the vector contents may have been correct, the actual object contained by the vector did not have an operator<< specified.

抱怨的是,虽然迭代和打印向量内容的函数可能是正确的,但向量包含的实际对象没有指定运算符<<。

You need to have one.

你需要一个。

If you already have a method called Print() in your Department class, you could simply create an overload for operator<< as follows:

如果你的Department类中已经有一个名为Print()的方法,你可以简单地为operator < <创建一个重载,如下所示:< p>

std::ostream& operator<<(std::ostream& os, const Department& department) {
    os<<department.Print();
    return os;
}

I had prepared the following code before you posted your update. Maybe it can help you.

在您发布更新之前,我已准备好以下代码。也许它可以帮到你。

#include<iostream>
#include<vector>
#include<string>

class Department {
 public:
  Department(const std::string& name)
      : m_name(name) { }
  std::string name() const {
    return m_name;
  }
 private:
  std::string m_name;  
};


// If you were to comment this function, you would receive the
// complaint that there is no operator<< defined.
std::ostream& operator<<(std::ostream& os, const Department& department) {
  os<<"Department(\""<<department.name()<<"\")";
  return os;
}

// This is a simple implementation of a method that will print the
// contents of a vector of arbitrary type (not only vectors, actually:
// any container that supports the range-based iteration): it requires
// C++11.
template<typename T>
void show(const T& container) {
  for(const auto& item : container) {
    std::cout<<item<<std::endl;
  }
}

int main() {
  std::vector<Department> deps = {{"Health"}, {"Defense"}, {"Education"}};
  show(deps);
}

Compile with g++ example.cpp -std=c++11 -Wall -Wextra (I used OS X 10.7.4 and GCC 4.8.1) to get:

用g ++编译example.cpp -std = c ++ 11 -Wall -Wextra(我使用OS X 10.7.4和GCC 4.8.1)得到:

$ ./a.out 
Department("Health")
Department("Defense")
Department("Education")