基类中的重载输出运算符

Question

I have a number of classes that represent various computer components, each of which have an overloaded << operator declared as follows:

friend ostream& operator << (ostream& os, const MotherBoard& mb);

Each returns an ostream object with a unique stream describing that component, some of which are composed of other components. I decided to create a base class called Component in order to generate a unique id as well as some other functions that all the components will publicly derive. Of course, the overloaded << operator doesn't work with pointers to Component objects.

I was wondering how I would effect something like a pure virtual function that will be overwritten by each derived class's << operator so I could do something like:

Component* mobo = new MotherBoard();

cout << *mobo << endl;

delete mobo;

Also related to: overloading << operators and inherited classes

Answer 1

Maybe something like this:

#include <iostream>

class Component 
{
public:
    // Constructor, destructor and other stuff

    virtual std::ostream &output(std::ostream &os) const
        { os << "Generic component\n"; return os; }
};

class MotherBoard : public Component
{
public:
    // Constructor, destructor and other stuff

    virtual std::ostream &output(std::ostream &os) const
        { os << "Motherboard\n"; return os; }
};

std::ostream &operator<<(std::ostream &os, const Component &component)
{
    return component.output(os);
}

int main()
{
    MotherBoard mb; 
    Component &component = mb;

    std::cout << component;
}