c – 使用const_cast的自动类型推断不起作用

在我的工作中,const_cast的使用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>中写出所有这种类型的混乱.表达式,特别是如果Clutter非常长.

我的第一个想法是编写const_cast<>(myType),但是我的编译器无法推导出myType的非const类型.所以我想帮助我的编译器和我编写以下方法,编译.

#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,程序给了我输出6 12而不是预期的6 6,我真的不明白？

我的做法有什么问题？

从 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.

所以你拥有的是未定义的行为.

同样令人感兴趣的是cv type qualifiers的这张纸条.

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.