在对象的生命周期中，"this"指针的值是否恒定? [英] Is the value of `this` pointer constant during the object's lifetime?

问题描述

在特定对象的生存期内， this 指针的值是否保证是恒定的?我无法想象情况会发生变化，但不知道我是否没有错过任何事情.

Is the value of this pointer guaranteed to be constant during a lifetime of a particular object? I can't imagine a case where it would change, but don't know whether I am not missing something.

推荐答案

在特定对象的生存期内， this 指针的值是否保证是恒定的?

Is the value of this pointer guaranteed to be constant during a lifetime of a particular object?

是.

以用户 Aconcagua 的说法: this 指针始终是在 ¹ 上调用了该函数的对象的地址值.因此，问题等同于:

As user Aconcagua puts it: the value of this pointer always is the value of the address of the object on which the function was called on¹. So the question is equivalent with:

对象可以在整个生命周期内更改其内存地址吗?

Can an object change its memory address over life time?

根据 lifetime ² 的定义，这是不可能的.对象的生存期从获取对象的时间开始或之后开始，直到释放对象时结束.

This is not possible, by definition of lifetime². The lifetime of an object begins when or after its storage is obtained and ends before of when it is released.

¹⁾ [class.this]/1

在非静态( [class.mfct] )成员函数的主体中，关键字 this 是 prvalue ，其值是指向要为其调用函数的对象的指针.

In the body of a non-static ([class.mfct]) member function, the keyword this is a prvalue whose value is a pointer to the object for which the function is called.

²⁾ [basic.life]/1 (重点是我的)

²⁾ [basic.life]/1 (emphasis mine)

对象或引用的生存期是对象或引用的运行时属性.如果变量是默认初始化的，则该变量被称为具有空虚的初始化；如果它是类类型或其(可能是多维)数组，则该类类型具有琐碎的默认构造函数.类型为 T 的对象的生存期始于:

The lifetime of an object or reference is a runtime property of the object or reference. A variable is said to have vacuous initialization if it is default-initialized and, if it is of class type or a (possibly multi-dimensional) array thereof, that class type has a trivial default constructor. The lifetime of an object of type T begins when:

获得
• 存储，并且具有正确的对齐方式和大小类型 T 的，并且
• 它的初始化(如果有的话)已完成(包括空虚初始化)( [dcl.init] )，除了如果对象是其并集成员或其子对象，则其生存期仅在联合成员是联合中的初始化成员( [dcl.init.aggr] ， [class.base.init] )，或如 [class.union] .

• storage with the proper alignment and size for type T is obtained, and
• its initialization (if any) is complete (including vacuous initialization) ([dcl.init]), except that if the object is a union member or subobject thereof, its lifetime only begins if that union member is the initialized member in the union ([dcl.init.aggr], [class.base.init]), or as described in [class.union].

类型为 T 的对象 o 的生​​存期:

The lifetime of an object o of type T ends when:

• 如果 T 是非类类型，则对象被破坏，或者
• 如果 T 是类类型，则析构函数调用开始，或者
• 对象所占用的存储空间已释放，或被未嵌套在 o ( [intro.object] >).

• if T is a non-class type, the object is destroyed, or
• if T is a class type, the destructor call starts, or
• the storage which the object occupies is released, or is reused by an object that is not nested within o ([intro.object]).

这篇关于在对象的生命周期中，"this"指针的值是否恒定?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！