t****n
发帖数: 15 | 1 Any one can help explaining in the following code,why pd1 points to the
start of the D object while pd2 points to the start of B subobject.
class A {/*...*/};
class B {/*...*/};
class D : public A, public B {/*...*/};
void f(B* pb)
{
D* pd1 = reinterpret_cast(pb);
D* pd2 = static_cast(pb);
}
f(new D); | t****t
发帖数: 6806 | 2 1. pd2 will point to the start of D object (new'ed in calling function), not
pd1.
2. practically speaking, the value of pd1 should be equal to pb, that is,
point to the start of B subobject. however strictly speaking, the result of
pd1 is not specified in standard. it is only known that reinterpret_cast
(reinterpret_cast(pb)) == pb.
【在 t****n 的大作中提到】
: Any one can help explaining in the following code,why pd1 points to the
: start of the D object while pd2 points to the start of B subobject.
: class A {/*...*/};
: class B {/*...*/};
: class D : public A, public B {/*...*/};
: void f(B* pb)
: {
: D* pd1 = reinterpret_cast(pb);
: D* pd2 = static_cast(pb);
: }
| N*********y
发帖数: 105 | 3 reinterpret_cast是強行翻譯，所以直接把pb指向的內存塊當成D*類型。reinterpret_
cast前后的內存起始地址一樣，所以pb和pb1指向同一位置。
static_cast靜態的嘗試做“合理”的翻譯。編譯器發現D是B的繼承類，并且D的起始地
址比B的起始地址相差A的大小，所以編譯器會把pb的起始地址減去A的大小來作為pd2的
地址。
【在 t****n 的大作中提到】
: Any one can help explaining in the following code,why pd1 points to the
: start of the D object while pd2 points to the start of B subobject.
: class A {/*...*/};
: class B {/*...*/};
: class D : public A, public B {/*...*/};
: void f(B* pb)
: {
: D* pd1 = reinterpret_cast(pb);
: D* pd2 = static_cast(pb);
: }
| t****n
发帖数: 15 | 4 Thanks thrust and NoDealToday.
Yes, that's what I thought.
But this example is given by Bjarne Stroustrup in his New Casts Revisited (
google New Casts Revisited, in the section 4). Maybe it is a typo?
not
of
*>
【在 t****t 的大作中提到】
: 1. pd2 will point to the start of D object (new'ed in calling function), not
: pd1.
: 2. practically speaking, the value of pd1 should be equal to pb, that is,
: point to the start of B subobject. however strictly speaking, the result of
: pd1 is not specified in standard. it is only known that reinterpret_cast
: (reinterpret_cast(pb)) == pb.
| t****t
发帖数: 6806 | 5 i guess it's a typo.
【在 t****n 的大作中提到】
: Thanks thrust and NoDealToday.
: Yes, that's what I thought.
: But this example is given by Bjarne Stroustrup in his New Casts Revisited (
: google New Casts Revisited, in the section 4). Maybe it is a typo?
:
: not
: of
: *>
|
|
