How to access data or functions of the derived class if it was declared as the base class?

[Titan]

Hi all,

In Delphi the following code will work:
(xx[n-1]as TLibr).XEarth=x x[1].xm*(-1.0);
where xx is defined as a array of class TBody, and it has n members;
Tlibr is the derived class of Tbody, and Xearth is its private data.

How to write the corresponding code in c++ ?

Thanks,

[tom_usenet]

Re: How to access data or functions of the derived class if it was declared as the base class?

On 30 Jun 2003 02:05:37 -0700, amaths@sohu.com (Titan) wrote:
[color=blue]
>Hi all,
>
>In Delphi the following code will work:
>(xx[n-1]as TLibr).XEarth=x x[1].xm*(-1.0);
>where xx is defined as a array of class TBody, and it has n members;
>Tlibr is the derived class of Tbody, and Xearth is its private data.
>
>How to write the corresponding code in c++ ?[/color]

If Xearth is private, you can't access it. It it isn't private, then,
firstly you'll need an array of TBody* rather than TBody (an array of
TBody only contains TBody elements, and not elements derived from
TBody), and secondly the code should look something like this:

The set up code looks something like this:
TBody* xx[n]; //or TBody** xx = new TBody*[n];
xx[n-1] = new TLibr;


and here's the transcription of your code:
dynamic_cast<TL ibr&>(*(xx[n-1])).XEarth = xx[1]->xm * -1.0;

It will throw an exception if xx[n-1] isn't an instance of TLibr.

Tom