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

问题描述

为什么rvalues没有内存地址？程序执行时是不是加载到RAM中，或者是指存储在处理器寄存器中的值？

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（为什么rvalues没有内存地址？）有点困惑。价值是一种表达方式。 表达式没有地址：对象具有地址。询问为什么不能将运算符的地址应用于rvalue表达式会更正确？

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?"

答案相当简单：您只能取一个对象的地址，并不是所有的rvalue表达式引用对象（例如，表达式 42 具有一个值，但不引用一个对象）。

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rvalue表达式引用对象，但这样的对象缺少持久性。由rvalue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（您可以通过在临时对象上调用成员函数来轻松发现这个对象; 这个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表达式之间的根本区别。 Lvalue表达式是指具有持久性的对象：一个lvalue表达式所指向的对象超越单个表达式。

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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