“值初始化”是什么意思？ [英] What does 'value initializing' something mean?

问题描述

可能重复：

如果我有一个类，例如：

If I have a class for example:

class Info
{
   int x;
   int y;
};

我用来创建一个对象，

Info *p = new Info();

信息旁边的括号是否意味着值初始化？与此不同的是， Info * p = new Info; ？

Does the brackets beside Info mean i'm value initializing it? How does it different from this, Info *p = new Info; ?

我知道有一个问题值初始化意味着将某些东西初始化为零？

I know there is a question which differentiate between different meanings in new and old C++ language but I want to know the semantic difference between default and value initialization e.g. Does value initialization means initializing something to zero?

推荐答案

声明的变量可以是零初始化， 默认初始化。

A declared variable can be Zero Initialized, Value Initialized or Default Initialized.

在您的示例中：

Info *p = new Info();    <------- Value Initialization
Info *p = new Info;      <------- Default Initialization

C ++ 03 Standard 8.5 / 5定义每个：

The C++03 Standard 8.5/5 aptly defines each:

要初始化类型T的对象意味着：

To zero-initialize an object of type T means:

- 如果T是标量类型（3.9），则将对象设置为转换为T的值0（零）;

- 如果T是非联合类类型，则每个非静态数据成员并且每个基类子对象

是零初始化的;

- 如果T是联合类型，则对象的第一个命名数据成员是零初始化的;

- 如果T是数组类型，则每个元素都进行零初始化;

- 如果T是引用类型，则不执行初始化。

— if T is a scalar type (3.9), the object is set to the value of 0 (zero) converted to T;
— if T is a non-union class type, each nonstatic data member and each base-class subobject
is zero-initialized;
— if T is a union type, the object’s first named data member is zero-initialized;
— if T is an array type, each element is zero-initialized;
— if T is a reference type, no initialization is performed.

要默认初始化类型T的对象意味着：

- 如果T是非POD类类型（第9节），调用T的默认构造函数（如果T没有可访问的默认构造函数，则
初始化不成功）;

- 如果T是数组类型，每个元素是缺省初始化的;

- 否则，对象是零初始化的。

To default-initialize an object of type T means:
— if T is a non-POD class type (clause 9), the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);
— if T is an array type, each element is default-initialized;
— otherwise, the object is zero-initialized.

要值初始化类型T的对象意味着：

- 如果T是类类型）和用户声明的构造函数（12.1），则调用T的默认
构造函数（如果T没有可访问的
默认构造函数，则初始化不成功）;

- 如果T是一个没有用户声明的构造函数的非union类型类型，那么T的每个非静态
数据成员和基类组件都被初始化;

- if T是一个数组类型，然后每个元素被初始化;

- 否则，对象是零初始化的

To value-initialize an object of type T means:
— if T is a class type (clause 9) with a user-declared constructor (12.1), then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);
— if T is a non-union class type without a user-declared constructor, then every non-static data member and base-class component of T is value-initialized;
— if T is an array type, then each element is value-initialized;
— otherwise, the object is zero-initialized

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