I try to find address of this pointer, but this code is showing a strange
error:

我试图找到此指针的地址，但此代码显示了一个奇怪的错误：

#include <iostream>
using namespace std;
class Base
{
    public:
        void test()
        {
            void *address_of_this =&this;
            cout<<address_of_this<<endl;
        }
};

int main()
{   Base k;
    k.test();

    return 0;
}   //error non-lvalue in unary'&'   

Can you explain this error ?

Also point that what is illegal in taking address of this?

你能解释一下这个错误吗？还指出，拿这个地址什么是违法的？

this is a pointer containing the address to the "current object". It is not a variable that is stored somewhere (or could even be changed), it is a special keyword with these properties.

这是一个包含指向“当前对象”的地址的指针。它不是存储在某个地方(甚至可以更改)的变量，而是具有这些属性的特殊关键字。

As such, taking its address makes no sense. If you want to know the address of the "current object" you can simply output:

因此，取它的地址是没有意义的。如果您想知道“当前对象”的地址，只需输出：

std::cout << this;

or store as

或存储为

void* a = this;

Quoting the 2003 C++ standard:

引用2003年的C++标准：

5.1 [expr.prim] The keyword this names a pointer to the object for which a nonstatic member function (9.3.2) is invoked. ... The type of the expression is a pointer to the function’s class (9.3.2), ... The expression is an rvalue.

5.3.1 [expr.unary.op] The result of the unary & operator is a pointer to its operand. The operand shall be an lvalue or a qualified_id.

To put it simply, & requires an lvalue. this is an rvalue, not an lvalue, just as the error message indicates.

简单地说，&需要一个左值。正如错误消息所示，这是一个右值，而不是左值。

this refers to the current object by using it's address.

它通过使用当前对象的地址来引用该对象。

In your problem, there are two errors:

在您的问题中，有两个错误：

• this is not an lvalue.

  这不是左值。

  
  
  

  The & requires an lvalue. lvalues are those that can appear on on the left-hand side of an assignment (variables, arrays, etc.).

  &需要左值。左值是那些可以出现在赋值左侧的值(变量、数组等)。

  
  
  

  Whereas this is a rvalue. rvalues can not appear on the left-hand side (addition, subtraction, etc.).

  然而，这是一个正确的价值。右值不能出现在左侧(加法、减法等)。

  
  
  

  Reference: C++ Rvalue References Explained.

  参考：C++右值参考解释。




• A hidden error which I'd like to also mention is thus:

  我还想提到的一个隐藏错误是：

  
  
  

  address_of_this is actually receiving an address of an address.

  Address_of_This实际上是在接收一个地址的地址。

  
  
  

  Basically, &this is translated into something like &&object or &(&object).

  基本上，&这被翻译成类似&&Object或&(&Object)之类的东西。

Basically, think of this as &object (but only to remember because it is not that true).

基本上，将其视为&Object(但只是为了记住，因为它并不是那么正确)。

this is a prvalue.

这是原价。

In other words, it's computed on the fly when needed, and not stored in the memory otherwise. Thus it doesn't have a persistent address/location for you to take.

换句话说，它是在需要时动态计算的，而不是存储在内存中。因此，它没有一个持久的地址/位置供您使用。