Re: Question about inheritance in c++

"Bo Persson" <>
Sun, 11 Mar 2007 12:08:23 +0100
<> wrote:

Hello everyone,

I wrote:

class CA{

CA() {number = 1;}
~CA() {}
int number;

class CB : public CA
CB(){number = 2;}
void foo(){

void main()
CA* a1 = new CA();
((CB*) a1)->foo();

OK, i pass compilation phase & runtime phase the output was
1. why i pass the runtime phase? CA class have no "uid" member.

You used a C-style cast here:

((CB*) a1)->foo();

That is a very powerful tool, telling the compiler to just "shut up and do

You are not asking the compiler to convert a1 into a CB*, you tell the
compiler that it already IS a CB*.

2. how can i protect this code and make this program fail in the
compilation phase?

You shouldn't tell lies to the compiler. :-)

If you had tried the C++ way, and done a static_cast<CB*>(a1), the compiler
would have told you that it cannot do that. You told it to do it anyway!

Bo Persson

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