为什么没有地址有地址？ [英] Why don't rvalues have an address?

问题描述

为什么rvalue没有内存地址？

Why don't rvalues have a memory address? Are they not loaded into the RAM when the program executes or does it refer to the values stored in processor registers?

推荐答案

您的问题是否正确？ （为什么rvalues有内存地址？）有点困惑。右值是一种表达式。 没有地址： 为什么不能将运算符的地址应用到右值表达式？

Your question ("Why don't rvalues have a memory address?") is a bit confused. An rvalue is a kind of expression. Expressions don't have addresses: objects have addresses. It would be more correct to ask "why can one not apply the address-of operator to an rvalue expression?"

这个问题的答案很简单：你只能取一个对象的地址，并不是所有的右值表达式都引用对象（例如，表达式 42 有一个值，而不是一个对象）。

The answer to that is rather simple: you can only take the address of an object and not all rvalue expressions refer to objects (for example, the expression 42 has a value but does not refer to an object).

一些右值表达式引用对象，但这样的对象缺少持久性。由右值表达式引用的对象是一个临时对象，并在创建它的表达式的末尾被销毁。这样的对象确实有地址（你可以通过调用一个临时对象的成员函数来轻松发现这个对象; this 指针必须指向临时对象，因此临时对象必须有一个地址）。

Some rvalue expressions do refer to objects, but such objects lack persistence. An object referred to by an rvalue expression is a temporary object and is destroyed at the end of the expression in which it is created. Such objects do indeed have addresses (you can easily discover this by calling a member function on a temporary object; the this pointer must point to the temporary object and thus the temporary object must have an address).

这是lvalue表达式和rvalue表达式的根本区别。 Lvalue表达式指具有持久性的对象：左值表达式引用的对象超出单个表达式。

This is the fundamental difference between lvalue expressions and rvalue expressions. Lvalue expressions refer to objects that have persistence: the object to which an lvalue expression refers persists beyond a single expression.

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