何时使用 reinterpret_cast? [英] When to use reinterpret_cast?

问题描述

我对 reinterpret_cast 与 static_cast 的适用性有点困惑.从我读到的一般规则是，当类型可以在编译时解释时使用静态转换，因此使用 static 这个词.这也是 C++ 编译器在内部用于隐式转换的转换.

I am little confused with the applicability of reinterpret_cast vs static_cast. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static. This is the cast the C++ compiler uses internally for implicit casts also.

reinterpret_casts 适用于两种场景:

• 将整数类型转换为指针类型，反之亦然
• 将一种指针类型转换为另一种.我得到的一般想法是这是不可移植的，应该避免.

我有点困惑的地方是我需要的一种用法，我从 C 调用 C++，C 代码需要保留 C++ 对象，所以基本上它包含一个 void*.void * 和 Class 类型之间应该使用什么类型转换?

Where I am a little confused is one usage which I need, I am calling C++ from C and the C code needs to hold on to the C++ object so basically it holds a void*. What cast should be used to convert between the void * and the Class type?

我见过 static_cast 和 reinterpret_cast 的用法?虽然从我一直在阅读的内容看来 static 更好，因为转换可以在编译时发生?虽然它说使用 reinterpret_cast 从一种指针类型转换为另一种?

I have seen usage of both static_cast and reinterpret_cast? Though from what I have been reading it appears static is better as the cast can happen at compile time? Though it says to use reinterpret_cast to convert from one pointer type to another?

推荐答案

C++ 标准保证以下内容:

The C++ standard guarantees the following:

static_cast 指向和来自 void* 的指针会保留地址.即，下面的a、b和c都指向同一个地址:

static_casting a pointer to and from void* preserves the address. That is, in the following, a, b and c all point to the same address:

int* a = new int();
void* b = static_cast<void*>(a);
int* c = static_cast<int*>(b);

reinterpret_cast 仅保证如果您将指针转换为不同的类型，然后 reinterpret_cast 将其恢复为原始类型，您会得到原始值.所以在下面:

reinterpret_cast only guarantees that if you cast a pointer to a different type, and then reinterpret_cast it back to the original type, you get the original value. So in the following:

int* a = new int();
void* b = reinterpret_cast<void*>(a);
int* c = reinterpret_cast<int*>(b);

a 和 c 包含相同的值，但 b 的值未指定.(在实践中，它通常包含与 a 和 c 相同的地址，但这在标准中没有指定，在具有更复杂内存系统的机器上可能不是这样.)

a and c contain the same value, but the value of b is unspecified. (in practice it will typically contain the same address as a and c, but that's not specified in the standard, and it may not be true on machines with more complex memory systems.)

对于与 void* 之间的转换，应该首选 static_cast.

For casting to and from void*, static_cast should be preferred.

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