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Is This Valid C++?

Posted on 1998-06-29
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Last Modified: 2010-04-01
Environment Visual C++ 5.0.

This compiles and appears to run OK but I was wondering whether it is valid (or good) C++. And if not is there a better way to do it?

class COther
{

protected:
      int x;
      int y;

public:
      COther();
      ~COther();
      virtual void set_values(int px,int py)
      {
            x = px;
            y = py;
      }
};

class A
{

protected:
      COther* other_class;

public:
      virtual void do_work()
      {
            other_class = new COther;
            other_class->set_values(2,4);
      }
};

class CNewOther : public COther
{
      int z;

public:
      CNewOther();
      ~CNewOther();
      virtual void set_values(int px,int py)
      {
            y = px;
            x = py;
            z = y*x;
      }
};

class B : public A
{
      virtual void do_work()
      {
            other_class = new CNewOther;
            other_class->set_values(2,4);
      }
};

This is a simple example of the actual code that has been written. It just struck me that this might potentially cause problems because the declared pointer is not the same as the instantiated type for the other_class object.

Any comments?
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Question by:sdj
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1 Comment
 
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Accepted Solution

by:
cmw earned 50 total points
ID: 1166775
Yes, this is valid. It works because you declare the set_values method virtual. So code is inserted to find out what the pointer points to, and to call the correct method. Leave out the virtual, and the compiler will assume that type of the pointer is allways correct, and try to call COther::set_values(). The virtual needs only to be specified at the root level, but I prefer to mention it through the hierarchy.

As to the question if it can be done differently, well I suppose you think of all sorts of ways of doing this, but it really depends on what you are trying to achieve. In general, Objects of classes should encapsulate the behaviour for which they are responsible. You do not mention what your objective is, so this isn't as straightforward.
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