[英]Opposite of const_cast
I have an std::vector<int*> v
and I'd like to prevent further writes to it.我有一个
std::vector<int*> v
并且我想防止进一步写入它。 The C++ compiler does not accept this C++ 编译器不接受这个
const std::vector<const int*>& w = v;
but it accepts this但它接受这个
const std::vector<const int*>& w = reinterpret_cast<const std::vector<const int*>&>(v);
The latter does work with Microsoft's compiler, meaning that the int*
inside v
and const int*
inside w
have the same addresses in memory.后者确实适用于微软的编译器,这意味着
v
中的int*
和w
中的const int*
在 memory 中具有相同的地址。
Does this work by chance, as an unspecified behavior, or is it valid C++?这是偶然的,作为一种未指定的行为,还是有效的 C++? Does it work with all types inside the vector, like
std::vector<std::shared_ptr<int>>
?它是否适用于向量内的所有类型,例如
std::vector<std::shared_ptr<int>>
? If invalid, is there another way to do this cast?如果无效,还有其他方法可以进行此转换吗?
I know I could also copy the vector, but I'd like to avoid that, since my vectors are pretty big.我知道我也可以复制向量,但我想避免这种情况,因为我的向量很大。
This is Undefined Behavior.这是未定义的行为。
std::vector<const int*>
and std::vector<int*>
are two different classes (generated by the same template, but that is irrelevant). std::vector<const int*>
和std::vector<int*>
是两个不同的类(由同一个模板生成,但这无关紧要)。 They cannot alias each other and you cannot reinterpret_cast
between them.它们不能相互别名,并且您不能在它们之间
reinterpret_cast
。
My solution is to use std::span
:我的解决方案是使用
std::span
:
const std::span s{const_cast<const int* const*>(v.data()), v.size()};
This will create a const std::span<const int* const>
.这将创建一个
const std::span<const int* const>
。
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