具体来说，标准在哪里声明修改 const 对象是未定义的行为？

Question

众所周知，以下示例会表现出未定义的行为：

T const x = T();
T& r = any_suitable_conversion_to_Tref(x); // fine
r = T(); // UB

const_cast 已由 cppreference 确认：

const_cast makes it possible to form a reference or pointer to non-const type that is actually referring to a const object or a reference or pointer to non-volatile type that is actually referring to a volatile object. Modifying a const object through a non-const access path and referring to a volatile object through a non-volatile glvalue results in undefined behavior.

但是，它没有提到例如c 风格的转换，它不引用标准（cppreference 通常从不引用）。

C++ 标准到底在哪里禁止这样做？

Answer 1

C++17 标准在第 10 章 "Declarations" [dcl.type.cv] 10.1.7 下声明：

Except that any class member declared mutable (10.1.1) can be modified, any attempt to modify a const object during its lifetime (6.8) results in undefined behavior.

具体来说，标准在哪里声明修改 const 对象是未定义的行为？

Where, specifically, does the standard state that modifying a const object is undefined behaviour?

c++

constants

object

language-lawyer