C ++将原始表转换为另一个表类型 [英] C++ cast raw table to another table type

问题描述

我想写类似于C ++ 11中的 std :: array 类。为了做到这一点我是
声明一个类型 char 在这个类里面的表，后来我想调用
placement new 在这个表上之后，我想使用表作为类型 T 的常规表，这里有麻烦。

一般变量如：

类型 char（&）[size] ，如果是这样，我想使用 reinterpret_cast 在这个表上将它转换为类型的表，我实际上使用，所以或多或少我会像我的代码看起来像这样：

  char tab [sizeof（T）* size]; 
 T tabT [size] = reinterpret_cast< T（&）[size]>（tab）; 
 //使用tabT更多的代码
  

但是在这个上下文中， $ c> char * 类型。原因，为什么我认为它可以工作是能够写以下模板函数

 模板< typename T，size_t size& 
函数（T（& table）[size]）{
 //做与T类型和尺寸大小的表连接的东西。 
} 
  

我知道我可以做到这一点没有这个奇特的魔法，要知道，为什么它不工作。

所以我的问题是：有一种方法来做我想做的事情，有什么更优雅的方式上面的工作？

PS：我不声明类型T的原始表： T tab [size] 因为我不能创建元素，没有没有
参数的构造函数。

解决方案

不真正帮助你：

  char标签[sizeof（T）* size]; 
 T tabT [size] = reinterpret_cast< T（&）[size]>（tab）; 
  

由于数组不可复制，所以代码实例化时不会编译。至少你需要使用

  T（& tabT）[size] = reinterpret_cast< T（& ）[Size]>（tab）;但是，我建议不要将未初始化的元素存储为 char  
 
 
 数组开始。只需使用嵌套数组使用 union ：
  template< typename T，int Size> 
类数组
 {
联合数据{
数据（）{} 
 T值[大小]; 
} data; 
 public：
 array（）{/ *适当初始化元素* /} 
〜array（）{/ *销毁初始化元素* /} 
 // ... 
}; 
  
 
I want to write class similar to the std::array from C++11. To do this I am
declaring a table of type char inside this class and later I would like to call
placement new on this table After that I would like to use table as if it was regular table of type T and here comes the trouble.

Generally variable like:
char tab[size]; 
Is of type char(&)[size] and if that's so I would like to use reinterpret_cast on this table to cast it to table of type, that I am in fact using, so more or less I would like my code to look like this:
char tab[sizeof(T)*size];
T tabT[size] = reinterpret_cast<T(&)[size]>(tab);
// more code using tabT
However in this context tab is seen as char* type. Reason, why I thought it could work is ability to write following template function
template <typename T, size_t size>
function(T(&table)[size]){
    //do stuff connected with table of type T and size size.
}
I know I could do this without this fancy magic here, but I just want to know, why it does not work.

So my question is: Is there a way to do the thing I want to do and is there any more elegant way to do mentioned job?

PS: I do not declare raw table of type T like : T tab[size], because I wouldn't be able to create elements, where there is no constructor without
arguments.
解决方案
The cast doesn't really help you:
char tab[sizeof(T)*size];
T tabT[size] = reinterpret_cast<T(&)[size]>(tab);
Since arrays aren't copyable this code doesn't compile when instantiated. At the very least you'd need to use
T (&tabT)[size] = reinterpret_cast<T(&)[Size]>(tab);
However, I'd recommend not to store the uninitialized elements as char array to start with. Just use a union with a nested array:
template <typename T, int Size>
class array
{
    union Data {
        Data() {}
        T values[Size];
    } data;
public:
    array() { /* initialize the elements appropriately */ }
    ~array() { /* destroy the initialized elements */ }
    // ...
};


                        
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