c++ - 为什么编译器在数组为零的情况下不推导出模板参数？

Question

我已阅读以下链接如何通过模板函数计算数组的大小:

• How does this “size of array” template function work? [duplicate]
• Can someone explain this template code that gives me the size of an array? [duplicate]

• Magic arguments in function templates

  但是这个技巧在数组为零的情况下不起作用。为什么下面的代码不正确？ 例如，在线编译器 ideone 会打印以下错误消息:

error: no matching function for call to 'size_of_array(int [0])'
std::size_t num = size_of_array(arr);

#include <cstddef>
template <typename T, std::size_t N>
inline std::size_t size_of_array( T (&)[N] ) {
   return N;
}
int main()
{
  int arr[0]={};
  std::size_t num = size_of_array(arr);
}

Answer 1

来自标准草案 n4296，§8.3.4 数组:

In a declaration T D where D has the form

D1 [ constant-expression ] attribute-specifier-seq

and the type of the identifier in the declaration T D1 is “derived-declarator-type-list T”, then the type of the identifier of D is an array type;

...

If the constant-expression is present, it shall be a converted constant expression of type std::size_t and its value shall be greater than zero.

所以您的代码无效。