Some simple question, that require simple answers:
How can I force the implementation of methods in a class, like the Java's interfaces, if possible?
Plus, how do I declare an abstract class?
What is the relation between this and virtual functions?
And how do the protected fields behave (I read the tutorial but didn't understand well)?
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Last edited by Micko; 07-07-2004 at 02:29 PM.
>>How can I force the implementation of methods in a class
Declare a function (method) as virtual or pure virtual, and overload it in a derived class (actually, if you declare an object of the derived class then I don't think you need to declare the function as virtual at all).
>>Plus, how do I declare an abstract class?
Any class with a pure virtual function is an abstract class.
>>What is the relation between this and virtual functions?
A virtual function is one that is meant to be overloaded. If you declare a pointer to a base class, then call the base class's virtual function, then the derived class's function will be called.
>>And how do the protected fields behave
Makes it so only the class itself and its derived classes can access the members declared as protected.
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Declaring it as virtual does not mean it must be reimplemented. Declare it as pure virtual:
Code:class A { public: virtual void foo( ) = 0; // Pure virtual. Must be reimplemented in anything to be instantiated. };
So this is a pure virtual function, and must be implemented in derived classes, right? Without the "= 0", it would be simply a virtual function, and the class abstract...Originally Posted by Zach L.
But does it really have to be 0 or can be any number? What is that number suposed to do?
I don't believe the class would be abstract without the "= 0". And yes, it has to be 0, although I don't think it really does anything except tell you that it's a pure virtual function. Maybe 0 is symbolic for nothingness, i.e. there's no function definition.Without the "= 0", it would be simply a virtual function, and the class abstract...
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The class would not be abstract (or rather, not an abstract data type [ADT]) without the '= 0'. A class with a pure virtual cannot be instantiated. And, yes, it must be 0.
just to note, " = 0" is nothing more than a tag that the compiler notices. If it sees this in a class, and sees you instantiating an object of that class, it's supposed to yell at you. I used to think that it would be declaring that function pointer to NULL, and when you define it in child classes, it would change the pointer for that class, but I was informed otherwise.
A final thing... (no need to make another thread)
Imagine I have the following class:
Can I declare an operator to make operation like this?Code:template<typename T> class Array{ private: T *array; uint _length; public: Array(uint capacity = 0) :_length(capacity){ array = new T[capacity]; } ~Array(){ delete array;_length=0; } T operator[](uint idx) const; //more operators uint length() const; };
Array<int> a(3);
a[0] = 5;//<<--operator
Last edited by xErath; 07-07-2004 at 11:15 PM.
You'd need to return a T& instead of just T.
Last edited by Hunter2; 07-08-2004 at 09:51 AM.
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I didn't understand well..
I have this to do, e.g.:Code:template<typename T> T Array<T>::operator[](uint idx) const{ return array[idx]; }
Array<int> a(3);
int n = a[2];
But I want to add an operator to do also:
a[2] = n;
Try that (and you have to change the function in the class declaration too).Code:template<typename T> T& Array<T>::operator[](uint idx){ return array[idx]; }
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That worked very well!! Thank you
No problemYou do know how and why it works though, right?
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Look at this thread for some explanation of why it works as it does: http://cboard.cprogramming.com/showthread.php?t=54632
