const_cast在C ++中的行为 [英] behavior of const_cast in C++

问题描述

这是我的问题，问题是在注释

Here is my problem, the problem is in comments

const int a = 5;
const_cast<int&>(a)=7; //throw over const attribute in a,and assign to 7
std::cout<<a<<std::endl; //why still out put 5!!!!!!!!!!

谁能告诉我为什么，有些书籍会考虑这些问题来推荐？
谢谢！

Who can tell me why, and some books account these problems to recommend ? Thanks!

推荐答案

如果你这样做的方式是未定义的行为。如果您想以定义的方式查看 const_cast<> 的效果：

As-written the way you're doing this is undefined behavior. If you wanted to see the effects of const_cast<> in a defined manner:

int a = 5;                  // note: not const. regular object.
const int& cref = a;        // const-reference to same object.
cref = 7;                   // illegal. cref is a const reference.
const_cast<int&>(cref) = 7; // legal. the original object a is not const.

只有 的原因是定义的行为是由于非const原始变量的性质， a 。你不能接受一个直接的const 对象，只是抛弃的常量，这是你的代码做的。 （至少已经多次向我解释过）。

The only reason this is defined behavior is due to the non-const nature of the original variable, a. You cannot take an outright-const object and simply cast away the const-ness, which is what your posted code did. (at least as it has been explained to me on several occasions).

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