Overloading << operator to print vector contents - c++

Question

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.
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.
Snippet of error:
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!

Answer 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.
You need to have one.
If you already have a method called Print() in your Department class, you could simply create an overload for operator<< as follows:
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.
#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:
$ ./a.out
Department("Health")
Department("Defense")
Department("Education")