Hello, I have an object called XXX previously derived from CDocument in
my MDI project.
Later, I create an concrete class called Subject. And I let XXX to have
multiple inheritance from Subject (Subject is an object with protected
constructor)
The problem is, whenever I used dynamic_cast to cast a Subject pointer
to XXX (I am quite sure Subject pointer is actually pointing to XXX), a
visual c++ runtime error will occur.
void fun(Subject *s) {
XXX *var = dynamic_cast(s);
var->hehehe();
}
However, when I try to do this:
void fun(Subject *s) {
XXX *var = (XXX *)(s);
var->hehehe();
}
everything just go fine. may i noe why this happen? is this bug related
to something called dynamic creation?
thanks you.
cheok 2 1737 yc*****@gmail.com wrote: Hello, I have an object called XXX previously derived from CDocument in my MDI project.
Later, I create an concrete class called Subject. And I let XXX to have multiple inheritance from Subject (Subject is an object with protected constructor)
Hmm, does that mean something like:
class XXX : public Subject, public CDocument
? Sometimes a single line of code can say more than a thousand words.
The problem is, whenever I used dynamic_cast to cast a Subject pointer to XXX (I am quite sure Subject pointer is actually pointing to XXX),
Well, dynamic_cast is the one to use if you are not sure.
a visual c++ runtime error will occur.
In which line?
void fun(Subject *s) { XXX *var = dynamic_cast(s);
That'd be a syntax error. dynamic_cast expects a type to cast to.
var->hehehe();
You didn't check whether var is a null pointer or not. If the dynamic_cast
fails, the returned value is a null pointer, in which case the above line
would probably crash.
}
However, when I try to do this:
void fun(Subject *s) { XXX *var = (XXX *)(s); var->hehehe(); }
everything just go fine. may i noe why this happen?
Hard to say with the small amount of (pseudo-)code you showed.
is this bug related to something called dynamic creation?
No idea what you mean by "something called dynamic creation".
<yc*****@gmail.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com... Hello, I have an object called XXX previously derived from CDocument in my MDI project.
Later, I create an concrete class called Subject. And I let XXX to have multiple inheritance from Subject (Subject is an object with protected constructor)
The problem is, whenever I used dynamic_cast to cast a Subject pointer to XXX (I am quite sure Subject pointer is actually pointing to XXX), a visual c++ runtime error will occur.
void fun(Subject *s) { XXX *var = dynamic_cast(s); var->hehehe(); }
XXX *var = dynamic_cast<XXX*>(s);
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