Classes / structs / Friendship / Essential C++
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#include <iostream>
class Animal {
private:
double weight;
double height;
public:
Animal(double w, double h) : weight(w), height(h) { }
friend void printWeight(Animal animal);
friend class AnimalPrinter;
// A common use for a friend function is to overload the operator<< for streaming.
friend std::ostream& operator<<(std::ostream& os, Animal animal);
};
void printWeight(Animal animal)
{
std::cout << animal.weight << "\n";
}
class AnimalPrinter
{
public:
void print(const Animal& animal)
{
// Because of the `friend class AnimalPrinter;" declaration, we are
// allowed to access private members here.
std::cout << animal.weight << ", " << animal.height << std::endl;
}
};
std::ostream& operator<<(std::ostream& os, Animal animal)
{
os << "Animal height: " << animal.height << "\n";
return os;
}
int main() {
Animal animal = {10, 5};
printWeight(animal);
AnimalPrinter aPrinter;
aPrinter.print(animal);
std::cout << animal;
}
Cpp
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