C ++投射为零 [英] C++ casts on zero

问题描述

你好，

以下陈述是合法的（0是实际的

a指针参数，可能是''0'和相关的

演员）？

MyClass * p = reinterpret_cast< MyClass *>（0）;

MyClass * p = static_cast< MyClass *>（0）;

谢谢和致以最诚挚的问候，

文杰

Hello,
Is the following statements legal (0 is actualy
a pointer parameter that could be ''0'' and relevant
to the casts) ?
MyClass* p = reinterpret_cast<MyClass*>(0);
MyClass* p = static_cast<MyClass*>(0);
Thanks and best regards,
Wenjie

推荐答案

2003年8月17日01:54： 20 -0700， go****@yahoo.com （文杰）写道：

On 17 Aug 2003 01:54:20 -0700, go****@yahoo.com (Wenjie) wrote:

以下陈述是否合法（0是实际的指针参数，可能是'0''并且与演员相关）？
MyClass * p = reinterpret_cast< MyClass *> ;（0）;
MyClass * p = static_cast< MyClass *>（0）;

Is the following statements legal (0 is actualy
a pointer parameter that could be ''0'' and relevant
to the casts) ?
MyClass* p = reinterpret_cast<MyClass*>(0);
MyClass* p = static_cast<MyClass*>(0);

这不是问题。


有什么问题？

That''s not the problem.

What is the problem?

Wenjie写道：

你好，

是以下的政治家ts legal（0是实际的
一个指针参数，可能是'0''并且与演员相关）？
MyClass * p = reinterpret_cast< MyClass *>（0）;
MyClass * p = static_cast< MyClass *>（0）;

Hello,
Is the following statements legal (0 is actualy
a pointer parameter that could be ''0'' and relevant
to the casts) ?
MyClass* p = reinterpret_cast<MyClass*>(0);
MyClass* p = static_cast<MyClass*>(0);

你想做什么？如果你想要一个所谓的NULL指针，那么就忘记

reinterpret_cast。为什么？因为那个是实现定义的。

并且NULL指针实现不一定是具有与包含零的整数相同的实现的指针。关于第二个演员::

它是不必要的。 0本身将自动转换为NULL指针

的正确类型。


WW aka Attila

What do you want to do? If you want a so-called NULL pointer, then forget
the reinterpret_cast. Why? Because that one is implementation defined.
And a NULL pointers implementation is not necessarily a pointer having the
same implementation as an integer containing zero. About the second cast::
it is unecessary. The 0 itself will automagically convert to a NULL pointer
of the right type.

WW aka Attila

Wenjie写道：

Wenjie wrote:

你好，

以下陈述合法


是的，虽然结果第一个是实现定义。

（0实际上是一个指针参数，可能是'0''并且与演员相关）？


我不明白。

MyClass * p = reinterpret_cast< MyClass *>（0）;


如果你想要一个空指针，请注意上面并不一定是
导致一个。它_might_导致一个所有位为零的指针，并且

指针_might_是一个空指针，但是不能保证。

MyClass * p = static_cast< MyClass *>（0）;

Hello,
Is the following statements legal
Yes, though the result of the first is implementation defined.
(0 is actualy a pointer parameter that could be ''0'' and relevant
to the casts) ?
I don''t understand that.
MyClass* p = reinterpret_cast<MyClass*>(0);
If you wanted a null pointer, note that the above doesn''t necessarily
lead to one. It _might_ lead to a pointer with all bits zero, and that
pointer _might_ be a null pointer, but that''s not guaranteed.
MyClass* p = static_cast<MyClass*>(0);

这与以下相同：


MyClass * p = 0;


使得pa空指针。

This is the same as:

MyClass* p = 0;

which makes p a null pointer.

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