为什么（int＆）0格式不正确？

Question

According to [expr.cast]/4, a C-style cast tries the following casts in order:

1. const_cast
2. static_cast
3. static_cast followed by const_cast
4. reinterpret_cast
5. reinterpret_cast followed by const_cast

The following cast is well-formed:

const_cast<int&>(static_cast<const int&>(0))

Yet both GCC and Clang reject the cast (int&)0 . Why?

Answer 1

The reason the cast (int&)0 is rejected is because you are trying to cast a literal as a reference which doesn't really make sense. The & operator expects a reference-able value and you cannot reference a literal. The compiler sees that you are casting a literal as an rvalue hence main.cpp:2:11: error: invalid cast of an rvalue expression of type 'int' to type 'int&'

This question doesn't really come down to the hierarchy of casts but instead the inability to cast literals as references.

Edit: Quick note, I am a little confused by your wording, is const_cast<int&>(static_cast<const int&>(0)); accepted by the compiler? It shouldn't due to casting an lvalue as an rvalue. If so I must've misunderstood the question and I'll recuse my answer.