c++ - 左值如何转换为右值

Question

int x = 8;
int y = x ;

这里左值如何充当右值？我知道这是一个愚蠢的问题，但我只想阐明我对右值和左值的概念。

Answer 1

通过左值到右值的转换。

您几乎可以在任何需要右值 和隐式左值 到右值 转换的地方使用左值将自动发生。

非正式地，此转换是“评估”或“获取”左值 所指对象的值。并非在所有情况下都严格如此。在未评估的上下文中，例如 sizeof 的操作数，将不会使用对象的值。

ISO/IEC 14882:2011 4.1 [conv.lval]:

A glvalue (3.10) of a non-function, non-array type T can be converted to a prvalue. If T is an incomplete type, a program that necessitates this conversion is ill-formed. If the object to which the glvalue refers is not an object of type T and is not an object of a type derived from T, or if the object is uninitialized, a program that necessitates this conversion has undefined behavior. If T is a non-class type, the type of the prvalue is the cv-unqualified version of T. Otherwise, the type of the prvalue is T.