Re: Question about inheritance in c++
On 3=D4 11=C8=D5, =CF =CE=E71=CA=B139=B7=D6, "Dotani...@gmail.com" <Dot=
ani...@gmail.com> wrote:
Hello everyone,
I wrote:
class CA{
public:
CA() {number = 1;}
~CA() {}
int number;
};
class CB : public CA
{
public:
CB(){number = 2;}
~CB()
void foo(){
uid++;
cout<<"uid:"<<uid<<endl;}
};
void main()
{
CA* a1 = new CA();
((CB*) a1)->foo();
}
OK, i pass compilation phase & runtime phase the output was
"uid:-23847298":
questions:
1. why i pass the runtime phase? CA class have no "uid" member.
2. how can i protect this code and make this program fail in the
compilation phase?
Thanks,thi
Dotan
Hello Dotan
Your programe maybe can't pass compilation phase,because the
compiler isn't able to find the declaration of "uid".I modified this
programe and let "uid" be the data menber of class CB.Then my programe
can get the same result as yours.The reason for this result is that
the constructor of class CB wasn't called,so "uid" wasn't initialized
and the value of it is uncertaint.
Changing the pointer of bass class to the ones of derived class is
unsafe except that you could make sure the object to which this
pointer points is derived class object.You can use operator
"dynamic_cast" to finish this work,but "dynamic_cast" requires the
bass class to have visual functions,because the compiler gets RTTI
from the visual tables.
Thanks
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