C++ output operator for abstract class - c++

Question

So I have an abstract class Product with fields name and price. There are a few classes that inherit from Product, and the reason Product is abstract is because these subclasses have to implement this function (defined in Product):
virtual std::string getCategory()=0;
Category is not a field, it just depends on which subclass we have and in some cases on the price.
Now I want an output operator for the subclasses of Product, but since I only want to print the name and price, I did this in Product.h:
friend std::ostream& operator<<(std::ostream& os, const Product& secondOperand);
And this in Product.cpp:
ostream& operator<<(ostream& outputStream, Product& secondOperand){
outputStream << "["<<secondOperand.getName()<<" "<<secondOperand.getPrice()<<"]"<<endl;
return outputStream;
}
Now I get this error in visual studio:
Error C2259: 'Product' : cannot instantiate abstract class
I don't want to implement this output for every subclass (cause then I have to literally copy everything which isn't ideal). Also, I started out with Product being not pure virtual, but then I had Linker errors for the getCategory() functions...

Answer 1

Nothing wrong with the approach, here's a sample which compiles and runs....
#include <string>
#include <iostream>
using namespace std;
class Product
{
public:
friend std::ostream& operator<<(std::ostream& os, const Product& secondOperand);
virtual ~Product() = 0;
string getName() { return "Product Name"; }
string getPrice() {return "£1.00"; }
virtual std::string getCategory()=0;
};
ostream& operator<<(ostream& outputStream, Product& secondOperand){
outputStream << "["<<secondOperand.getName()<<" "<<secondOperand.getPrice()<<"]"<<endl;
return outputStream;
}
Product::~Product() {}
class DerivedProduct : public Product
{
public:
DerivedProduct() {}
std::string getCategory() { return "Derived getCategory()"; }
};
int main(int argc, char *argv[])
{
DerivedProduct d;
cout << d.getCategory() << endl;
cout << d << endl;
return 0;
}