Thread: question on syntax

Q1. from // line 1, i see that is a destructor. but why virtual ? virtual is usued in inheritance .why in a class defunition ? is it just a syntax ?

You really need virtual functions whenever the class will be used as base class(the rule is if the class has any other virtual function, add the virtual destructor) . Fortunatly, the compilers I've used are able to flag this as a warning.

The reason why you need a virtual destructor is shown by this code

Code:

#include <iostream>
using namespace std;

class A {
public:
      virtual void a() { cout << "A" << endl; }
      // no virtual destructor
};
 
class B {
      int* items;
public:
      B() : items(new int[100]) { }
      ~B() { delete[] items; }
      virtual void a() { cout << "B" << endl; }
};

int main()
{
     A* a = new B;
 
     delete a;           // since a's destructor is not virtual, A's destructor is called not B's

     return 0;
}

b.A :: func1() // is it legal ? what does it mean ? //line 2

I don't think so.

I think what you mean by the code at the end is a call to the base class's function. You do that with something like this

Code:

class Sprite {
public:
       virtual void draw() {/*...*/ }
};

class BdSprite : public Sprite {
public:
       virtual void draw() { Sprite::draw(); }
};

This calls Sprite's draw, not BdSprite's, avoiding the infinite recursion that would otherwise occur.