问题描述

可能的重复:
什么时候应该使用static_cast、dynamic_cast和reinterpret_cast?

我在 c++ 中使用 c 函数，其中在 c 中作为 void 类型参数传递的结构直接存储相同的结构类型.

I'm using c function in c++, where a structure passed as a void type argument in c is directly stored that same structure type.

例如在 C 中.

void getdata(void *data){
    Testitem *ti=data;//Testitem is of struct type.
}

为了在 C++ 中做同样的事情，我使用 static_cast:

to do the same in c++ i use static_cast:

void foo::getdata(void *data){
    Testitem *ti = static_cast<Testitem*>(data);
}

当我使用 reinterpret_cast 它做同样的工作，转换结构

and when i use reinterpret_cast it does the same job, casting the struct

当我使用 Testitem *it=(Testitem *)data;

这也做同样的事情.但是使用这三个对结构有什么影响.

this does the same thing too. But how is the structure gets affected by using the three of them.

推荐答案

static_cast 是从一种类型到另一种类型的转换，它(直觉上)是在某些情况下可以成功并有意义的转换在没有危险演员的情况下.例如，您可以将 static_cast void* 转换为 int*，因为 void* 实际上可能指向int* 或 int 到 char，因为这样的转换是有意义的.但是，您不能将 static_cast int* 转换为 double*，因为这种转换仅在 int* 以某种方式被修改为指向 double*.

A static_cast is a cast from one type to another that (intuitively) is a cast that could under some circumstance succeed and be meaningful in the absence of a dangerous cast. For example, you can static_cast a void* to an int*, since the void* might actually point at an int*, or an int to a char, since such a conversion is meaningful. However, you cannot static_cast an int* to a double*, since this conversion only makes sense if the int* has somehow been mangled to point at a double*.

A reinterpret_cast 是表示不安全转换的强制转换，该转换可能将一个值的位重新解释为另一个值的位.例如，将 int* 转换为 double* 对 reinterpret_cast 是合法的，尽管结果未指定.类似地，使用 reinterpret_cast 将 int 转换为 void* 是完全合法的，尽管它不安全.

A reinterpret_cast is a cast that represents an unsafe conversion that might reinterpret the bits of one value as the bits of another value. For example, casting an int* to a double* is legal with a reinterpret_cast, though the result is unspecified. Similarly, casting an int to a void* is perfectly legal with reinterpret_cast, though it's unsafe.

static_cast 和 reinterpret_cast 都不能从某些东西中删除 const.您不能使用这些转换中的任何一个将 const int* 转换为 int*.为此，您将使用 const_cast.

Neither static_cast nor reinterpret_cast can remove const from something. You cannot cast a const int* to an int* using either of these casts. For this, you would use a const_cast.

(T) 形式的 C 样式转换被定义为尝试执行 static_cast，如果可能的话，退回到 reinterpret_cast> 如果这不起作用.如果绝对必须，它也会应用 const_cast.

A C-style cast of the form (T) is defined as trying to do a static_cast if possible, falling back on a reinterpret_cast if that doesn't work. It also will apply a const_cast if it absolutely must.

一般来说，你应该总是喜欢使用 static_cast 来进行安全转换.如果您不小心尝试执行未明确定义的强制转换，那么编译器将报告错误.仅当您所做的确实改变机器中某些位的解释时才使用 reinterpret_cast，并且仅当您愿意冒险执行 reinterpret_cast<时才使用 C 风格的强制转换/代码>.在您的情况下，您应该使用 static_cast，因为在某些情况下 void* 的向下转换是明确定义的.