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dynamic_cast operator in C++

dynamic_cast operator in C++# Programming - 葵花宝典

i*p2007-10-19 07:10

1 楼

How to understand this sentence.
The class of the object passed to the dynamic_cast operator must be part of
the hierarchy the object is being cast to.
To discuss it easily, I have following statements.
A *ap;
....
B *bp = dynamic_cast(ap);
1. Which class, A or B is "The class of the object passed to the dynamic_
cast operator"? I guess it is A.
2. Class B should be "the object is being cast to", right?

d*d2007-10-19 07:10

2 楼

right.

of

【在 i**p 的大作中提到】

: How to understand this sentence.
: The class of the object passed to the dynamic_cast operator must be part of
: the hierarchy the object is being cast to.
: To discuss it easily, I have following statements.
: A *ap;
: ....
: B *bp = dynamic_cast(ap);
: 1. Which class, A or B is "The class of the object passed to the dynamic_
: cast operator"? I guess it is A.
: 2. Class B should be "the object is being cast to", right?

d*d2007-10-19 07:10

3 楼

dynamic_cast 一般是向下cast。
这句话的意思是指，B得是A的子类或孙子类....

of

【在 i**p 的大作中提到】

e*w2007-10-19 07:10

4 楼

To make it a valid dynamic_cast, B should be descendant of A.
The object pointed by ap should be an object of B or B's descendant.

of

【在 i**p 的大作中提到】

i*p2007-10-19 07:10

5 楼

So far no arguement that B得是A的子类或孙子类....
But can "the part" be interpreted as inherence?

【在 e*****w 的大作中提到】

: To make it a valid dynamic_cast, B should be descendant of A.
: The object pointed by ap should be an object of B or B's descendant.
:
: of

P*f2007-10-19 07:10

6 楼

Besides downcast,
dynamic_cast is also used to support "cross cast" in MI.

To make it a valid dynamic_cast, B should be descendant of A.
The object pointed by ap should be an object of B or B's descendant.
of

【在 e*****w 的大作中提到】

: To make it a valid dynamic_cast, B should be descendant of A.
: The object pointed by ap should be an object of B or B's descendant.
:
: of

e*w2007-10-19 07:10

7 楼

you're right. if the class hierarchy is A -> C as long as ap points to object of C (or its descendant),
then we can do this dynamic_cast, too.

【在 P*****f 的大作中提到】

: Besides downcast,
: dynamic_cast is also used to support "cross cast" in MI.
:
: To make it a valid dynamic_cast, B should be descendant of A.
: The object pointed by ap should be an object of B or B's descendant.
: of

i*p2007-10-19 07:10

8 楼

Is "Class C, the class of the object that ap points to" the same as "The
class of the object passed to the dynamic_cast operator"?

【在 e*****w 的大作中提到】

: you're right. if the class hierarchy is A -> C : as long as ap points to object of C (or its descendant),
: then we can do this dynamic_cast, too.

e*w2007-10-19 07:10

9 楼

yes.

【在 i**p 的大作中提到】

: Is "Class C, the class of the object that ap points to" the same as "The
: class of the object passed to the dynamic_cast operator"?

i*p2007-10-19 07:10

10 楼

Make it more clear of my understanding.
A *ap = new C;
B *bp = dynamic_cast(ap);
"The class of the object passed to the dynamic_cast operator" is A, not C,
even though ap points to object of C.

【在 e*****w 的大作中提到】
: yes.