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

From: Morten Gulbrandsen (Morten.Gulbrandsen_at_rwth-Aachen.DE)
Date: 02/05/05 

Date: Sat, 05 Feb 2005 17:37:55 +0100

Hello

something is wrong with my gcc compiler

here is my code

=== snip ===

template <class T> // declare the template and the parameter
class Array // the class being parameterized
{
public:
   // constructors
   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.GetSize(); i++)
       output << "[" << i << "] " << theArray[i] << endl;
   return output;
}

== snip ===

g++ -ansi -pedantic -Wall -o ostream_operator_problem.out
ostream_operator_problem.cpp -L /opt/sfw/gcc-3/lib/ -R
/opt/sfw/gcc-3/lib/ -lstdc++

g++ -o ostream_operator_problem.out ostream_operator_problem.cpp -L
/opt/sfw/gcc-3/lib/ -R /opt/sfw/gcc-3/lib/ -lstdc++

ostream_operator_problem.cpp:46: warning: friend declaration `std::ostream&
  operator<<(std::ostream&, Array<T>&)' declares a non-template function

ostream_operator_problem.cpp:46: warning: (if this is not what you intended,
  make sure the function template has already been declared and add <> after
  the function name here) -Wno-non-template-friend disables this warning
Undefined first referenced
symbol in file

operator<<(std::basic_ostream<char, std::char_traits<char> >&,
Array<int>&)/var/tmp//ccMap1MM.o

ld: fatal: Symbol referencing errors. No output written to
ostream_operator_problem.out

collect2: ld returned 1 exit status

Please help

gcc -v
Reading specs from /opt/sfw/gcc-3/lib/gcc-lib/i386-pc-solaris2.9/3.3.2/specs
Configured with: ../gcc-3.3.2/configure --prefix=/opt/sfw/gcc-3
--with-ld=/usr/ccs/bin/ld --with-as=/usr/ccs/bin/as --without-gnu-ld
--without-gnu-as --enable-shared
Thread model: posix
gcc version 3.3.2

bash-2.05$ uname -X
System = SunOS
Node = Hirschgraben15-23
Release = 5.9
KernelID = Generic_112234-12
Machine = i86pc
BusType = <unknown>
Serial = <unknown>
Users = <unknown>
OEM# = 0
Origin# = 1
NumCPU = 1

best regards

Morten Gulbrandsen

// Using Operator ostream

#include <iostream>

using namespace std;

const int DefaultSize = 10;

class Animal
{
public:
        Animal(int);
        Animal();
        ~Animal() {}
        int GetWeight() const { return itsWeight; }
        void Display() const { 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 parameterized
{
public:
        // constructors
        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.GetSize(); 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];
        for (int i = 0; i<size; i++)
                pType[i] = 0;
}

// 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;
}

int main()
{
        bool Stop = false; // flag for looping
        int offset, value;
        Array<int> theArray;

        while (!Stop)
        {
                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;
}

/*

g++ -ansi -pedantic -Wall -o ostream_operator_problem.out
ostream_operator_problem.cpp -L /opt/sfw/gcc-3/lib/ -R
/opt/sfw/gcc-3/lib/ -lstdc++

g++ -o ostream_operator_problem.out ostream_operator_problem.cpp -L
/opt/sfw/gcc-3/lib/ -R /opt/sfw/gcc-3/lib/ -lstdc++

ostream_operator_problem.cpp:46: warning: friend declaration `std::ostream&
    operator<<(std::ostream&, Array<T>&)' declares a non-template function

ostream_operator_problem.cpp:46: warning: (if this is not what you
intended,
    make sure the function template has already been declared and add <>
after
    the function name here) -Wno-non-template-friend disables this warning
Undefined first referenced
  symbol in file

operator<<(std::basic_ostream<char, std::char_traits<char> >&,
Array<int>&)/var/tmp//ccMap1MM.o

ld: fatal: Symbol referencing errors. No output written to
ostream_operator_problem.out

collect2: ld returned 1 exit status

*/

/*
Your Comeau C/C++ test results are as follows:

Comeau C/C++ 4.3.3 (Aug 6 2003 15:13:37) for ONLINE_EVALUATION_BETA1
Copyright 1988-2003 Comeau Computing. All rights reserved.
MODE:strict errors C++

In strict mode, with -tused, Compile succeeded (but remember, the Comeau
online compiler does not link).

*/

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