新的A v.s.新A（） [英] new A v.s. new A()

问题描述

你好，

之间有什么区别：

A * p =新A;

和

A * p =新A（）;

？


我知道这里一定要讨论，但只是

不容易搜索。顺便说一句，我认为

A a;

类似于建筑商电话有关的新A？

（默认的construtor电话？）对吗？ br />

和

A a（）;

只是一个功能声明？

谢谢你，最好的问候，

文杰

Hello,
Is there any difference between:
A* p = new A;
and
A* p = new A();
?

I know it must have been dicussed here, but just
not easy to search. BTW, I think
A a;
is alike new A as far as constructor call concerned
(default construtor call?) Right?

And
A a();
is just a function declaration?
Thanks and best regards,
Wenjie

推荐答案

" Wenjie" <去**** @ yahoo.com>写道...

"Wenjie" <go****@yahoo.com> wrote...

之间有什么区别：
A * p = new A;
和
A * p = new A（）;
？


课程没有区别，POD有差异

：前者保留未初始化的对象，

后者将其初始化为零。

我知道它一定是在这里被讨论过，但只是不容易搜索。顺便说一句，我认为
A a;
就像建设者电话有关的新A一样
（默认的construtor电话？）对吗？


这是一个声明（在某些情况下的定义）

对象'a'的A类型。如果它是'a'定义，对象

是默认初始化的，对于一个类来说意味着它的c-tor

被调用，是的。

和
A a（）;
只是一个函数声明？

Is there any difference between:
A* p = new A;
and
A* p = new A();
?
There is no difference for classes, there is a difference
for POD: the former leaves the object uninitialised, the
latter zero-initialises it.
I know it must have been dicussed here, but just
not easy to search. BTW, I think
A a;
is alike new A as far as constructor call concerned
(default construtor call?) Right?
It''s a declaration (and a definition in certain circumstances)
of an object ''a'' of type A. If it''s a definition, the object
is default-initialised, which for a class means that its c-tor
is invoked, yes.

And
A a();
is just a function declaration?

是的，它是。

Victor

Yes, it is.
Victor

Wenjie写道：

Wenjie wrote:

您好，

之间有什么区别：
A * p =新A;
和
A * p =新A（）;
？


是的，在某些情况下有所不同。

它与POD'有关（POD =普通的旧数据结构，
基本上是一个只用内置类型构建的类或结构

并且没有成员函数，简而言之：一个结构，因为它是

ment in C）


new A

创建一个新的A类POD对象并让所有成员保持未初始化


new A（）

创建一个新的POD对象，类型为A，但是0初始化所有成员。

A a（）;
只是一个函数声明？

Hello,

Is there any difference between:
A* p = new A;
and
A* p = new A();
?
Yes, there is a difference in certain circumstances.
It has to do with POD''s (POD = plain old data structure,
basically a class or a struct built from only builtin types
and having no member functions, in short: a struct as it was
ment to be in C)

new A
creates a new POD-object of type A and leaves all members uninitialized

new A()
creates a new POD-object of type A but 0-initializes all members.
A a();
is just a function declaration?

是的。这是一个陷阱。


-

Karl Heinz Buchegger
kb ****** @ gascad.at

" Victor Bazarov" <五******** @ attAbi.com>在留言新闻中写道：vf ************ @ corp.supernews.com ...

"Victor Bazarov" <v.********@attAbi.com> wrote in message news:vf************@corp.supernews.com...

班级没有区别，


非POD课程（但你知道的。）

POD有差异：前者让对象未初始化，
后者将其初始化为零。

There is no difference for classes,
non-POD classes (but you knew that).
there is a difference
for POD: the former leaves the object uninitialised, the
latter zero-initialises it.

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