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undefined reference error -HELP!

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Join Date: Oct 2006

Posts: 232

Reputation: JRM will become famous soon enough

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JRM

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Posting Whiz in Training

undefined reference error -HELP!

Dec 18th, 2006

hello all.

This program is just a collection of functions to demonstrate various programming principles. What I'm
saying is that don't worry about the overall function-it ain't all that...

One of the principles is using a 'non member' friend function to display the output.
I added this to the public functions and it's definition appears just below the class declaration.

I get warning about it's status (OK), but then the fatal error is

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
templ2.cpp: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, Array<int>&)'
 
templ2.cpp: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, Array<int>&)'

the source:

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// Implementation of the Template Array
#include <iostream>
using namespace std;
const int DefaultSize =10;
 
//declare a simple Animal class so that we can create an
//array of animals
 
class Animal
{
    public:
        Animal(int) ;
        Animal();
        ~Animal() {}
        int GetWeight () const { return itsWeight;}
        void Display() const {std::cout << itsWeight;}
    private:
        int itsWeight;
};
 
Animal::Animal(int weight):
itsWeight(weight)
{ }
 
Animal::Animal():itsWeight(0)
{}
 
 
template <class T> //declare the template and the parameter
class Array       // the class being paramterized
{
    public:
        //costrucyors
        Array(int itsSize = DefaultSize);
        Array(const Array &rhs);
        ~Array() {delete [] ptype;}
 
        //operators
        Array& operator = (const Array&);
        T& operator [] (int offset) {return ptype[offset];}
        const T& operator[] (int offset) const
        {return ptype[offset];}
        //accessors
        int GetSize() const {return itsSize;}
        //template <class T>//compiler needs this if non member friend
        friend ostream& operator << (ostream&, Array<T>&);
 
 
 
    private :
        T *ptype;
        int itsSize;
};
 
template <class T>
ostream& operator << (ostream& output, Array<T>& theArray)
{
    for (int i = 0; i < theArray.itsSize; i++)
      output << "[" << i << "]" << theArray[i] <<endl;
 
    return output;
}
 
//implementations follow...
 
//implement the constructor
template <class T>
Array<T>::Array(int size):
itsSize(size)
{
    ptype = new T[size];
    //the constructors of the type created
    //should be of default value
}
 
//copy constructor
template <class T>
Array<T>::Array(const Array &rhs)
{
    itsSize =rhs.GetSize();
    ptype = new T[itsSize];
    for (int i=0; i<itsSize; i++)
        ptype[i] = rhs[i];
}
//operator=
 
template <class T>
Array<T>& Array<T>::operator=(const Array &rhs)
{
    if (this == &rhs)
        return *this;
    delete [] ptype;
    itsSize = rhs.GetSize();
    ptype = new T[itsSize];
    for (int i =0; i<itsSize; i++)
        ptype[i] =rhs[i];
    return *this;
}
 
//driver program
 
int main()
 
{
    bool Stop = false;  //looping flag
    int offset , value;
    Array<int> theArray;
    while (Stop = false)
    {
        cout << "Enter an offset (0-9)";
        cout << "and a value. (-1 to stop): ";
        cin >> offset >>value;
 
        if (offset < 0 )
            break;
        if (offset > 9)
        {
            cout << "*** Please use values between 0 and 9. ***\n";
            continue;
        }
        theArray[offset] = value;
    }
    cout << "\nHere's the entire array:\n";
    cout << theArray << endl;
 
    return 0;
}
// Implementation of the Template Array
#include <iostream>
using namespace std;
const int DefaultSize =10;

//declare a simple Animal class so that we can create an
//array of animals

class Animal
{
    public:
        Animal(int) ;
        Animal();
        ~Animal() {}
        int GetWeight () const { return itsWeight;}
        void Display() const {std::cout << itsWeight;}
    private:
        int itsWeight;
};

Animal::Animal(int weight):
itsWeight(weight)
{ }

Animal::Animal():itsWeight(0)
{}


template <class T> //declare the template and the parameter
class Array       // the class being paramterized
{
    public:
        //costrucyors
        Array(int itsSize = DefaultSize);
        Array(const Array &rhs);
        ~Array() {delete [] ptype;}

        //operators
        Array& operator = (const Array&);
        T& operator [] (int offset) {return ptype[offset];}
        const T& operator[] (int offset) const
        {return ptype[offset];}
        //accessors
        int GetSize() const {return itsSize;}
        //template <class T>//compiler needs this if non member friend
        friend ostream& operator << (ostream&, Array<T>&);
        
    
        
    private :
        T *ptype;
        int itsSize;
};

template <class T>
ostream& operator << (ostream& output, Array<T>& theArray)
{
    for (int i = 0; i < theArray.itsSize; i++)
      output << "[" << i << "]" << theArray[i] <<endl;
    
    return output;
}

//implementations follow...

//implement the constructor
template <class T>
Array<T>::Array(int size):
itsSize(size)
{
    ptype = new T[size];
    //the constructors of the type created
    //should be of default value
}

//copy constructor
template <class T>
Array<T>::Array(const Array &rhs)
{
    itsSize =rhs.GetSize();
    ptype = new T[itsSize];
    for (int i=0; i<itsSize; i++)
        ptype[i] = rhs[i];
}
//operator=

template <class T>
Array<T>& Array<T>::operator=(const Array &rhs)
{
    if (this == &rhs)
        return *this;
    delete [] ptype;
    itsSize = rhs.GetSize();
    ptype = new T[itsSize];
    for (int i =0; i<itsSize; i++)
        ptype[i] =rhs[i];
    return *this;
}

//driver program

int main()

{
    bool Stop = false;  //looping flag
    int offset , value;
    Array<int> theArray;
    while (Stop = false)
    {
        cout << "Enter an offset (0-9)";
        cout << "and a value. (-1 to stop): ";
        cin >> offset >>value;

        if (offset < 0 )
            break;
        if (offset > 9)
        {
            cout << "*** Please use values between 0 and 9. ***\n";
            continue;
        }
        theArray[offset] = value;
    }
    cout << "\nHere's the entire array:\n";
    cout << theArray << endl;
            
    return 0;
}

I'm sure you eagle -eyed pro's can spot the problem in a New York minute, but I've been straring at this too long!

Thanks in advance!

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Join Date: Aug 2005

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Ancient Dragon Ancient Dragon is offline

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Still Learning

Re: undefined reference error -HELP!

Dec 18th, 2006

My solution would be to write a public get function and use it in the loop instead of attempting to accessing the private member directly.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Join Date: Jun 2006

Posts: 7,649

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~s.o.s~

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Failure as a human

Re: undefined reference error -HELP!

Dec 18th, 2006

•

Originally Posted by JRM

I'm sure you eagle -eyed pro's can spot the problem in a New York minute, but I've been straring at this too long!

I don't blame you, since what you encountered is one of the C++ gotchas and not many starters know about it.

What you are trying to do here is to create a function which will befriend all the specializations of the Array class, which I don't think any compiler conforming with the standards will allow you to do.

There are some things which you have to do to get around this...

1. Forward declare the class, along with the templated overloaded function.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
template <class T> 
class Array ;
template <class T>
ostream& operator<< ( ostream&, Array<T>& ) ;
template <class T> 
class Array ;
template <class T>
ostream& operator<< ( ostream&, Array<T>& ) ;

2. Place <> after the overloaded operator to let the compiler know that this is a templated funcion you are tryign to code here (syntactic sugar...bleh). Something like:

 Help with Code Tags 
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template <class T> //declare the template and the parameter
class Array       // the class being paramterized
{
    public:
        ....
        friend ostream& operator<< <>(ostream&, Array<T>&);
    private :
        ....
};
template <class T> //declare the template and the parameter
class Array       // the class being paramterized
{
    public:
        ....
        friend ostream& operator<< <>(ostream&, Array<T>&);
    private :
        ....
};

For an interesting read look here.

I don't accept change; I don't deserve to live.

Jo Tujhe Jagaaye, Nindein Teri Udaaye Khwaab Hai Sachcha Wahi.
Nindon Mein Jo Aaye Jise To Bhul Jaaye Khawab Woh Sachcha Nahi.
Khwaab Ko Raag De, Nind Ko Aag De

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Join Date: Oct 2006

Posts: 232

Reputation: JRM will become famous soon enough

Solved Threads: 14

JRM

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Posting Whiz in Training

Re: undefined reference error -HELP!

Dec 24th, 2006

Yep! That's the way it works. Seems like alot of trouble to make the direct acess friend function to compile.

here's the final draft that compiles using the friend function.
Note that the template id operator <> is only used where is declared as a public function. The definition doesn't need it. That rather surprises me...

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
template <class T >
class Array;
 
template <class T>
ostream& operator << (ostream& , Array<T>& );
template <class T> //declare the template and the parameter
class Array       // the class being paramterized
 
 
{
    public:
        //costrucyors
        Array(int itsSize = DefaultSize);
        Array(const Array &rhs);
        ~Array() {delete [] ptype;}
 
        //operators
        Array& operator = (const Array&);
        T& operator [] (int offset) {return ptype[offset];}
        const T& operator[] (int offset) const
        {return ptype[offset];}
        //accessors
        int GetSize() const {return itsSize;}
 
        friend ostream& operator << <> (ostream&, Array<T>&);
 
 
 
    private :
        T *ptype;
        int itsSize;
};
 
 
template <class T >
ostream& operator << (ostream& output, Array<T>& theArray)
 
 
{
    for (int i = 0; i < theArray.itsSize; i++)
      output << "[" << i << "]" << theArray[i] <<endl;
 
    return output;
}
template <class T >
class Array;

template <class T>
ostream& operator << (ostream& , Array<T>& );
template <class T> //declare the template and the parameter
class Array       // the class being paramterized


{
    public:
        //costrucyors
        Array(int itsSize = DefaultSize);
        Array(const Array &rhs);
        ~Array() {delete [] ptype;}

        //operators
        Array& operator = (const Array&);
        T& operator [] (int offset) {return ptype[offset];}
        const T& operator[] (int offset) const
        {return ptype[offset];}
        //accessors
        int GetSize() const {return itsSize;}

        friend ostream& operator << <> (ostream&, Array<T>&);



    private :
        T *ptype;
        int itsSize;
};


template <class T >
ostream& operator << (ostream& output, Array<T>& theArray)


{
    for (int i = 0; i < theArray.itsSize; i++)
      output << "[" << i << "]" << theArray[i] <<endl;

    return output;
}

Thanks for your input!