所以什么是“这个”的类型。 ？为什么是“这个”不是左值？ [英] so what is the type of "this" ? Why is "this" not a lvalue?

问题描述

说对象是

  class A {
 public：void Silly（）{
 this = 0x12341234; 
} 
  

我知道我会得到编译器错误'这不是一个左值。 但是那不是一个暂时的。那么什么是this的假设声明？

编译器：在Mac上的GCC 4.2编译器。

对于某些类X，这个有类型 X * this; 你不允许赋值它，所以即使它实际上没有类型 X * const this ，它的行为几乎就像防止赋值去。正式来说，它是一个 prvalue ，这是一个类似于整数文本的类，因此尝试分配它大致相当于尝试分配一个不同的值到'a'或 10 。

>早期 C ++，这个是一个左值 - 分配给这处理一个对象的内存分配，类似于重载 new 和 delete 当时还支持）。

Say the object is

class A {
public :  void Silly(){
    this = 0x12341234;
}

I know I will get compiler error ' "this" is not a lvalue.' But then it is not a temporary either. So what is the hypothetical declaration of "this" ?

Compiler : GCC 4.2 compiler on mac.

解决方案

For some class X, this has the type X* this;, but you're not allowed to assign to it, so even though it doesn't actually have the type X *const this, it acts almost like it was as far as preventing assignment goes. Officially, it's a prvalue, which is the same category as something like an integer literal, so trying to assign to it is roughly equivalent to trying to assign a different value to 'a' or 10.

Note that in early C++, this was an lvalue -- assigning to this was allowed -- you did that to handle the memory allocation for an object, vaguely similar to overloading new and delete for the class (which wasn't supported yet at that time).

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