Thread: Overloading templated class operators

Having some trouble understanding how to overload operators (specifically << and >> ) for
a templated class.

Here's what I have in Attribute.h:

Code:

#include <iostream>

template <typename T>
class Primitive
{

    template<typename C> friend istream& operator>>(istream& in, Primitive<C>& p) { in >> p.data; return in; }
    template<typename C> friend ostream& operator<<(ostream& out, const Primitive<C>& p) { out << p.data; return out; }
  
    public:
    
        Primitive(T d) { data=d; }
        Primitive(Primitive& p) { data=p.getData(); }
        ~Primitive(){};
        T getData(){ return data; };
        
    private:
        T data;
    };

This is the main.cpp I use:

Code:

#include <cstdlib>
#include <iostream>
#include <Attribute.h>

int main(int argc, char *argv[])
{
    Attribute<int> aI(5);
    Attribute<string> aS("Bob");
    
    cout<<aI;
          
    system("PAUSE");
}

and these are the errors:

Code:

In file included from main.cpp:8:
I:/Dev-Cpp/include/c++/3.4.2/Primitive.h:7: error: expected init-declarator before '&' token
I:/Dev-Cpp/include/c++/3.4.2/Primitive.h:7: error: expected `;' before '&' token
I:/Dev-Cpp/include/c++/3.4.2/Primitive.h:8: error: expected init-declarator before '&' token
I:/Dev-Cpp/include/c++/3.4.2/Primitive.h:8: error: expected `;' before '&' token

I feel I may be a little over my head as I just got the hang of template classes and functions. I've read the few posts here that I could find with my meager script-fu, but I'm coming up short on understanding. Help?

So what you're saying is remove the friend qualifier?
I have a public getData() method and will make a public setData() method, although I was waiting until I had the output operator working.

I also just realized I was showing two versions of the same program. Primitive.h and Attribute.h are exactly the same, save for the names. I had been working on an Attribute class and came across someone else's similar problem using a Primitive class. Looked just like what I was doing so I tried working with that.

Anyway, having removed the friend qualifier I'm still getting the same problem:

Code:

C:/Dev-Cpp/include/Primitive.h:6: error: expected constructor, destructor, or type conversion before '&' token

C:/Dev-Cpp/include/Primitive.h:6: error: expected `;' before '&' token

C:/Dev-Cpp/include/Primitive.h:11: error: expected constructor, destructor, or type conversion before '&' token

C:/Dev-Cpp/include/Primitive.h:11: error: expected `;' before '&' token

using:

Code:

#include <iostream>

template <typename T>
class Primitive
{
    template<typename C> istream& operator>>(istream& in, Primitive<C>& p)
    {
        in << p.setData();
        return in;
        }
    template<typename C> ostream& operator<<(ostream& out, const Primitive<C>& p)
    {
        out << p.getData();
        return out;
        }

    public:

        Primitive(T d) { data=d; }
        Primitive(Primitive& p) { data=p.getData(); }
        ~Primitive(){};
        T getData(){ return data; };
        void setData(T d) { data = d;}

    private:
        T data;
    };

I'm thinking that I'm putting the definition in the wrong place but every tutorial I can find on the subject uses the friend method.

Nevermind, realized I was missing several ';' at the end of my functions. I've fixed that and am left with:

Code:

#include <iostream>

template <typename T>
class Primitive
{
    public:
        Primitive(){};
        Primitive(T d): data(d) { };
        Primitive(Primitive& p) { data=p.getData(); };
        ~Primitive(){};
        T getData(){ return data; };
        void setData(T d) { data = d;};
        T istream& operator>>(istream& in, Primitive<T>& p)  //Line 13
        {
            in << p.setData();
            return in;
            };
        T ostream& operator<<(ostream& out, Primitive<T>& p)  //Line 18
        {
            out << p.getData();
            return out;
            };

    private:
        T data;
    };

and the errors:

Code:

C:/Dev-Cpp/include/Primitive.h:13: error: expected `;' before '&' token

C:/Dev-Cpp/include/Primitive.h:18: error: expected `;' before '&' token

You have to specify the std namespace for istream and ostream. You also have to remove the T from the return values of the functions. Finally, you have to move those functions outside of the class, they should not be members or Primitive.

Actually, that's just a start, also look at the operator>> function, you have to re-do that a little. There might be other errors as well, but start by fixing those.

Bingo! I had added 'using namespace std' since my post, but I didn't realize that the functions needed to be out of the class. Works like a charm now, thanks