C++ Q39: throw new (C1) - 未名空间MITBBS历史存档

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C++ Q39: throw new (C1)

C++ Q39: throw new (C1)# JobHunting - 待字闺中

c*e2010-08-13 07:08

1 楼

class A {};
class B : A {};
void foo() { throw new B; }
Which of the following catch statements successfully catches the exception
foo throws?
a) catch (A* e) and catch (B* e)
b) catch (A e) and catch (B e)
c) catch (A* e)
d) catch (B* e)
e) catch (A e)
I have no answer. Help, please.

s*t2010-08-13 07:08

2 楼

why a is not right?

s*t2010-08-13 07:08

3 楼

异常处理我一点不懂。
刚才试了一下，如果throw new A也不能catch B*

s*t2010-08-13 07:08

4 楼

which is subtype and super type?
I think you might be wrong. Consider the following change, what is your
answer?
class A {};
class B : A {};
void foo() { throw new A; }
Which of the following catch statements successfully catches the exception
foo throws?
a) catch (A* e) and catch (B* e)
b) catch (A e) and catch (B e)
c) catch (A* e)
d) catch (B* e)
e) catch (A e)

M*q2010-08-13 07:08

5 楼

that's exactly why A* can catch new B(), i think

c*e2010-08-13 07:08

6 楼

I think it is d). You throw a pointer to B, then you need to catch it. Here
to catch a pointer to A is not enough.

s*t2010-08-13 07:08

7 楼

this makes perfect sense

Here

【在 c**********e 的大作中提到】

: I think it is d). You throw a pointer to B, then you need to catch it. Here
: to catch a pointer to A is not enough.

x*y2010-08-13 07:08

8 楼

Sorry, you are right...A* can only be caught by A* but B* can be caught by A
* and B*...

【在 s*****t 的大作中提到】

: which is subtype and super type?
: I think you might be wrong. Consider the following change, what is your
: answer?
: class A {};
: class B : A {};
: void foo() { throw new A; }
: Which of the following catch statements successfully catches the exception
: foo throws?
: a) catch (A* e) and catch (B* e)
: b) catch (A e) and catch (B e)

x*y2010-08-13 07:08

9 楼

Sorry, I made a mistacke, it should be a.

【在 s*********t 的大作中提到】

: why a is not right?

s*t2010-08-13 07:08

10 楼

it's not a.
u just got the right answer but ur explaination wasn't

【在 x***y 的大作中提到】

: Sorry, I made a mistacke, it should be a.

x*y2010-08-13 07:08

11 楼

Sorry, I made a mistake...A* can only be caught by A*, B* can be caught by A
* and B* as the thrown B* is also A* object....

【在 s*********t 的大作中提到】

: 异常处理我一点不懂。
: 刚才试了一下，如果throw new A也不能catch B*

x*y2010-08-13 07:08

12 楼

It shoudl be a, my original answer is wrong....All the public inheritence
relations in c++ satisfy that the derived object is also a base object. here
, a B* is thrown, which is also a A*, that is why it can caught by both A*
and B*.
I verified in my programme and the throw new B can be caught by catch(A*).

【在 s*********t 的大作中提到】

: it's not a.
: u just got the right answer but ur explaination wasn't

x*y2010-08-13 07:08

13 楼

Sorry, I made a mistacke, you are right....

【在 M******q 的大作中提到】

: that's exactly why A* can catch new B(), i think