什么是虚设此外在该＆QUOT的目的;元素＆QUOT数;宏？ [英] What's the purpose of dummy addition in this "number of elements" macro?

问题描述

的Visual C ++ 10附带的stdlib.h中除其他外包含此宝石：

Visual C++ 10 is shipped with stdlib.h that among other things contains this gem:

template <typename _CountofType, size_t _SizeOfArray>
char (*__countof_helper(UNALIGNED _CountofType (&_Array)[_SizeOfArray]))[_SizeOfArray];

#define _countof(_Array) (sizeof(*__countof_helper(_Array)) + 0)

它使用一个聪明的模板伎俩演绎数组大小和被传递到prevent指针 __ countof 的

什么是 0 + 的宏定义的目的是什么？它解决什么问题呢？

What's the purpose of + 0 in the macro definition? What problem does it solve?

推荐答案

从<一个引用STL href=\"http://channel9.msdn.com/Forums/TechOff/567789-template-countof-confusion-question\">here

我做了这个改变;我通常不破解CRT，但是这一次是
  不重要的。该+ 0沉默虚假警告C6260：sizeof的* sizeof的
  通常是错的。您是否打算使用字符数或字节
  算不算？从/分析时，有人写_countof（ARR）* sizeof的（T）。

I made this change; I don't usually hack the CRT, but this one was trivial. The + 0 silences a spurious "warning C6260: sizeof * sizeof is usually wrong. Did you intend to use a character count or a byte count?" from /analyze when someone writes _countof(arr) * sizeof(T).

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