c++ - 使用 const_cast 的自动类型推导不起作用

Question

在我的工作中使用const_cast在某些情况下是不可避免的。

现在我必须 const_cast一些非常复杂的类型，实际上我不想在 const_cast<Clutter> 中写下所有这些类型困惑表达式，尤其是如果 Clutter很长。

我的第一个想法是写 const_cast<>(myType) , 但我的编译器无法推断出 myType 的非常量类型.所以我想帮助我的编译器，我设计了以下编译方法。

#include <stdlib.h>
#include <iostream>

int main(int, char**) {
    const int constVar = 6;
    using T = typename std::remove_cv<decltype(constVar)>::type;
    auto& var = const_cast<T&>(constVar);
    var *= 2;
    std::cout << &constVar << " " << &var << "\n"; // Same address!
    std::cout << constVar << " " << var << "\n";
    return EXIT_SUCCESS;
}

不幸的是，程序给出了输出 6 12而不是预期的 6 6 ，我真的不明白？

我的方法有什么问题？

Answer 1

来自 const_cast 的文档:

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.

所以你所拥有的是未定义的行为。

同样有趣的是来自 cv type qualifiers 的注释.

const object - an object whose type is const-qualified, or a non-mutable subobject of a const object. Such object cannot be modified: attempt to do so directly is a compile-time error, and attempt to do so indirectly (e.g., by modifying the const object through a reference or pointer to non-const type) results in undefined behavior.