ali wrote:
Quote:
Hi,
>
I'm have a base class with a virual function toString. All the derived
classes will have to implement this function.
>
Here's the code I have used:
>
//in base.h
virtual string* toString();
|
class base {
public:
virtual string toString() const = 0; // note: returns object not
// pointer. pure virtual
// requires derived
// classes to implement
};
Quote:
>
//in base.cpp
string* base::toString()
{
return new string("Error: using base class toString method");
}
|
implementation should be deleted. By making toString() pure virtual,
you can't call it through the base class, you can't even instantiate
an object that doesn't have an overridden toString().
above is now illegal, assuming the pure virtual. Implement derived
class derived : public base
{
public:
string toString() const { /* some implementation */ }
};
derived d;
Quote:
|
cout<<*(base.toString()<<endl;
|
The pointer construct is not necessary once you return by value
cout << d.toString() << endl;
Quote:
I was wondering if there was a way i could use it so that in main.cpp
i could use something like:
>
cout<<base.toString()<<endl;
|
The above implementation is illegal because base has pure virtual
(abstract).
Quote:
I'm learning C++, and since I've programmed in Java most of the time,
its getting a little confusing.
|
Repeat after me. C++ is not Java. When possible, you don't want to
dynamically allocate objects.
Even better is to implement operator<< for base and children:
std::ostream& operator<<(std::ostream& os, const base& b)
{
os << b.toString();
return os;
}
This allows you to avoid the toString(), at least for output constructs.
Thus:
derived d;
std::cout << d << std::endl;
virtual function and string - help 
