problems overloading << operator

[nomad5000]

Hello!

I'm trying to overload the << operator but it just won't work

my code is the following:

the student.h file
 
#include <string>
#include <iostream>
 
using namespace std;
class student
{
  private:
    string name;
    string department;
  public:
    student(string n = "", string dep = 0)
    : name(n), department(dep) {}
 
    string get_name() const { return name; }
    string get_department () const { return department; }
    void set_name(const string& n) { name=n; }
    void set_department (const string& d) {department=d;}
    ostream& operator << (ostream& os, const student& s);
};
 
 

the student.cpp file
 
ostream& student::operator << (ostream& os, const student& s)
{
  return os<<s.get_name()<<'\t'<<s.get_department()<<endl;
}
 

main.cpp file
 
#include "student.h"
int main()
{
    student st("Bill Jones", "Zoology");
    cout<<st;
}
 

the compiler tells me the following error message:

"student.h": E2080 'student::operator <<(ostream &,const student &)' must be declared with one parameter at line 18

[JosAH]

You have to make your overloaded operator<< function a friend function because
the left operand of that expression insn't a object from your class (it's an ostream).

kind regards,

Jos

[nomad5000]

sorry about my ignorance, but exactly how do you declare a function a friend function

Thanks very much!!

Michael

[AdrianH]

sorry about my ignorance, but exactly how do you declare a function a friend function

Thanks very much!!

Michael

Put friend in front of it in the prototype in the class declaration. Make a prototype outside of the class declaration (before the class declaration). Define the function in your source file. Note that it is not a member of the class, so you do not specify the class scope when defining the function.


Adrian

[weaknessforcats]

The way your class is designed, you don't need a friend function at all.

Your code is:

the student.cpp file
 
ostream& student:: operator << (ostream& os, const student& s)
{
  return os<<s.get_name()<<'\t'<<s.get_department()<<endl;
}
 

Nothing in this code requires access to the class private data. It uses accessor functions instead. You need to:

1) remove the operator<< function prototype from your class
2) change this code to not be a member function:

the student.cpp file
 
ostream& operator << (ostream& os, const student& s)
{
  return os<<s.get_name()<<'\t'<<s.get_department()<<endl;
}
 

and things should work fine.

The only time you need a friend function is when the first argument cannot be a "this" pointer AND the function needs access to the class private data elements. This is not your situation.