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c++templateslinker-errorslnk2019

C++ linker errors, unresolved externals


Why am I getting linker errors when trying to compile this code, this is basically a code for a template class matrix that is complex & matrix is a square matrix so if size "3" is entered it means a matrix of [3][3] but somehow it gives me errors, any help?

#include <iostream>
#include <iomanip>
using namespace std;

template <class T>
class matrix
{
private:
  T** real;
  T** imag;
int size;
public:
  matrix(int = 0);
  friend ostream& operator<<(ostream& out, matrix<T>);
};

// constructor

template <class T>
matrix<T>::matrix(int length)
{
 size = length;

real = new T*[size];
for (int i = 0; i < size; i++)
    real[i] = new T[size];

imag = new T*[size];
for (int i = 0; i < size; i++)
    imag[i] = new T[size];

cout << "Enter real elements of matrix: ";
for (int i = 0; i < size; i++)
    for (int j = 0; j < size; j++)
        cin >> real[i][j];

cout << "Enter imag elements of matrix: ";
for (int i = 0; i < size; i++)
    for (int j = 0; j < size; j++)
        cin >> imag[i][j];
}

// functions defined here

template <class T>
ostream& operator<<(ostream& out, matrix<T> arg)
{
 out << showpos;
 for (int i = 0; i < arg.size; i++)
    for (int j = 0; j < arg.size; j++)
        out << arg.real[i][j] << arg.imag[i][j] << " ";
out << endl;
return out;
}

int main()
{
  matrix <int> obj1(3);
  cout << obj1;
}

Solution

  • Thank you everyone for help. seems like i needed the template because it was a non-member function of class matrix, following is the correct code. Sorry if I've done anything wrong while posting this question because in-fact this is first time I'm using stack overflow.

    #include <iostream>
    #include <iomanip>
    #include <cstdlib>
    using namespace std;
    
    // Class !
    
    template <class T> class matrix
    {
    private:
        T** real;
        T** imag;
        int size;
    public:
        matrix(int = 0);
        matrix(int,int);
    template <class T> friend ostream& operator<< <T>(ostream& out, matrix<T>);
    matrix operator+(matrix);
    matrix operator-(matrix);
    };
    
    // Constructor !
    
    template <class T> matrix<T>::matrix(int lenght, int dummy)
    {
    size = lenght;
    
    real = new T*[size];
    for (int i = 0; i < size; i++)
        real[i] = new T[size];
    
    imag = new T*[size];
    for (int i = 0; i < size; i++)
        imag[i] = new T[size];
    }
    
    template <class T> matrix<T>::matrix(int length)
    {
    size = length;
    
    real = new T*[size];
    for (int i = 0; i < size; i++)
        real[i] = new T[size];
    
    imag = new T*[size];
    for (int i = 0; i < size; i++)
        imag[i] = new T[size];
    
    cout << "Enter real elements of matrix >> \n";
    for (int i = 0; i < size; i++)
        for (int j = 0; j < size; j++)
            cin >> real[i][j];
    
    cout << "Enter imag elements of matrix: >> \n";
    for (int i = 0; i < size; i++)
        for (int j = 0; j < size; j++)
            cin >> imag[i][j];
    }
    
    // Main()
    
    
    int main()
    {
    int size;
    cout << "Enter Size: ";
    cin >> size;
    
    cout << "\nMatrix A created !" << endl;
    matrix <int> A(size);
    
    cout << "\nMatrix B created !" << endl;
    matrix <int> B(size);
    system("cls");
    
    cout << "Matrix A" << endl;
    cout << A;
    
    cout << "\nMatrix B" << endl;
    cout << B;
    
    cout << "\nMatrix A + B" << endl;
    cout << A + B;
    
    cout << "\nMatrix A - B" << endl;
    cout << A - B;
    }
    
    // Functions !
    
    template <class T> ostream& operator<<(ostream& out, matrix<T> arg)
    {
    out << showpos;
    for (int i = 0; i < arg.size; i++)
    {
        for (int j = 0; j < arg.size; j++)
        {
            out << arg.real[i][j] << arg.imag[i][j] << "i ";
        }
            out << endl;
    }
    return out;
    }
    
    template <class T> matrix<T> matrix<T>::operator+(matrix arg)
    {
    matrix<T> temp(size,0); // 0 is a inserted as dummy because I've overloaded             
    constructor of class
    
    for (int i = 0; i < size; i++)
    {
        for (int j = 0; j < size; j++)
        {
            temp.real[i][j] = real[i][j] + arg.real[i][j];
            temp.imag[i][j] = imag[i][j] + arg.imag[i][j];
        }
    }
    return temp;
    }
    
    template <class T> matrix<T> matrix<T>::operator-(matrix arg)
    {
    matrix<T> temp(size, 0); // 0 is a inserted as dummy because I've overloaded  
    constructor of class
    
    for (int i = 0; i < size; i++)
    {
        for (int j = 0; j < size; j++)
        {
            temp.real[i][j] = real[i][j] - arg.real[i][j];
            temp.imag[i][j] = imag[i][j] - arg.imag[i][j];
        }
    }
    return temp;
    }