Question

class apple
{
  public :
    operator orange () const { cout << "operator"; }
} ;
class orange
{
  public :
    orange (apple &x ){cout <<"constructor";}
};
void f(orange o)
{
  cout <<"function can accept only oranges ";
}
int main()
{
  apple a;
  f(a);
}

Output:
Compiler Error

Why does this code gives compiler error on g++ compiler? Why isn’t the constructor for orange called when function f is called?

Answer 1

You have a cyclic dependency:

class apple
{
public :
   operator orange () const { cout << "operator"; } //depends on orange
                                                    //shouldn't compile
} ;
class orange
{
public :
   orange (apple &x ){cout <<"constructor";} //depends on apple
};

I’m surprised you’re not getting compiler errors. Anyway, you need to define orange before you define apple, and you don’t need the operator orange:

class apple;
class orange
{
public :
   orange (apple &x ){cout <<"constructor";}
};
class apple
{
public :
};

This should work.