Field has incomplete type

Question

template <class Type>
class Punct {
    
protected:
    
    Type _x; // (1)
    Type _y; // (1)
    
public:

    Punct(Type = 0, Type = 0); // (2)
    ~Punct();
    inline Type getX() const { return _x; }
    inline Type getY() const { return _y; }
  
    inline void setX(Type x) { _x = x; }
    inline void setY(Type y) { _y = y; }
    inline void moveBy(int x, int y) { _x = x; _y = y; }

friend std::istream &operator>>(std::istream&ins, Punct<Type>& A);
friend std::ostream &operator<<(std::ostream&outs, const Punct<Type>& A);

};

These are the errors I get:

(1) - FIeld has incomplete type 'Type'

(2) - No viable conversion from int to type (and some add 3. Passing argument to parameter here)

Could you please tell me what is it that I'm doing wrong?

That code makes no sense. `Type` is a type, not a variable, so you cannot assign a value to it. You meant to add a variable name in your constructor. Show us the definition of `Type`. — Ed S., Apr 12 '13 at 20:27
@Teodora: it depends on the type you instantiate with. **show the code** — Cheers and hth. - Alf, Apr 12 '13 at 20:30
I was given some headers and as homework I have to implement the functions. At fist instead of 'type' it was int. I have a base class Shape which has derived classes such as Triangle, Square etc. (everything worked perfectly until I started the last task which was to parametrize the classes so that Triangle would have int Points and so on. I'm new to templates, I read some articles and I thought that this is how I should do it.) — Teodora, Apr 12 '13 at 20:32

gongzhitaao · Answer 1 · 2013-04-12T20:48:35.080

This code works for me. g++ 4.7.2 on Kubuntu 12.04.

By the way, do you have all the implementations of your Punct class in one file, i.e., the header file or you separate them into .h and .cpp?

#include <iostream>
using namespace std;

template <class Type>
class Punct {

protected:

    Type _x; // (1)
    Type _y; // (1)

public:

    Punct(Type = 0, Type = 0) {}; // (2) <- empty function body added
    ~Punct() {}; // <- empty function body added
    inline Type getX() const { return _x; }
    inline Type getY() const { return _y; }

    inline void setX(Type x) { _x = x; }
    inline void setY(Type y) { _y = y; }
    inline void moveBy(int x, int y) { _x = x; _y = y; }

    template<class T> // <- added
    friend std::istream &operator>>(std::istream&ins, Punct<T>& A);
    template<class T> // <- added
    friend std::ostream &operator<<(std::ostream&outs, const Punct<Type>& A);

};

// bogus function added
template<class T>
istream &operator>> (istream &i, Punct<T> &a)
{
    return i;
}

// bogus function added
template<typename T>
ostream &operator<< (ostream &i, const Punct<T>& a)
{
    return i;
}

int main()
{
    Punct<int> a;
}

Yes, I have implemented the not inline functions in the .cpp file, why? — Teodora, Apr 12 '13 at 21:02
@Teodora For template class, usually all implementation goes in header file. If not, much efforts are needed. see this post: http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file — gongzhitaao, Apr 12 '13 at 21:04
@Teodora: Templatized classes have to be fully defined (implemented) in header files. This restriction is imposed because of the way linkage works. Read [this question](http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file) for more information. — Alexander Shukaev, Apr 12 '13 at 21:06

Field has incomplete type

1 Answers1