是否可以有一个C ++类型占用0个字节 [英] Can there be a C++ type that takes 0 bytes

问题描述

我正在尝试声明一个占用零字节的C ++变量。它是联合的，我从int [0]类型开始。我不知道这是否实际上是零字节（尽管sizeof（int [0]）为0）。我需要一种更好的方法来声明一个0字节的类型，并希望可以将其类型定义为nullType或emptyType。该变量是一个并集，因此在最终存储器中仍然保留。我试着在无效的机会上尝试作废，但C ++抱怨。我使用的是Ubuntu 10.10，具有当前版本的内核和最新的GCC。
这是工会：

  union RandomArgumentTypesFirst 
 {
 uint uintVal; 
 nullType nullVal; 
} 
  

这是typedef：

  typedef int [0] nullType; 
  

编译器对typedef这么说：

 错误：变量或字段'nullVal'声明为voidmake [2]：
  

当我键入 int [0] 时，它可以工作。有建议吗？

编辑：
正如@fefe在评论中所说， int [0] 可以由编译器作为扩展提供。 GCC的网站上说默认情况下编译器具有许多扩展。

解决方案

typedef拼写错误：

  typedef int nullType [0];正如其他人指出的那样，您不能拥有大小为0的对象；但是，编译器可以（并且经常这样做）提供  Empty基类 优化。
 
 
 
 
 
  http://en.wikibooks.org/wiki / More_C％2B％2B_Idioms / Empty_Base_Optimization  
 
 
  http： //www.cantrip.org/emptyopt.html （空成员优化）
 
 
 
I'm trying to declare a C++ variable that takes up zero bytes. Its in a union, and I started with the type as int[0]. I don't know if that is actually zero bytes (although sizeof(int[0]) was 0). I need a better way to declare a 0 byte type, and hopefully one that can be typedefed to something like nullType or emptyType. The variable is in a union, so in the end memory is reserved anyway. I tried void on the off chance it would work, but C++ complained. I'm using Ubuntu 10.10, with a current version of the kernel, and an up-to-date GCC.
Here's the union:
union RandomArgumentTypesFirst
{
    uint uintVal;
    nullType nullVal;
}
And here is  the typedef:
typedef int[0] nullType;
The compiler says this about the typedef:
error: variable or field ‘nullVal’ declared voidmake[2]:
When I typed in int[0], it worked. Any suggestions?

EDIT:
As @fefe said in the comments, the int[0] may be provided as an extension by the compiler. GCC's website says that the compiler has many extensions by default.
解决方案
The typedef is misspelled:
typedef int nullType[0];
As others have pointed out, you cannot have an object of size 0; However, compilers can (and frequently do) provide the Empty Base Class optimization.


http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Empty_Base_Optimization
http://www.cantrip.org/emptyopt.html ("empty member" optimization)


                        
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