这个语句 std::__throw_out_of_range(__N("array::at")) 中的 __N() 是什么？

Question

我正在查看 array 头文件中 at() 函数的定义以消除一些疑问。这是定义-

reference                   //typedef for &value_type of array
at(size_type __n)           //size_type is typedef for size_t
{
    if (__n >= _Nm)        //_Nm is typedef for size of array
        std::__throw_out_of_range(__N("array::at"));   //what is __N(...) ?
    return _M_instance[__n];        //_M_instance[...] is variable of type std::array
}

那么，最后第三行的 N(...) 是什么？或者更具体地说，它有什么作用？

Answer 1

来自their source code

// This marks string literals in header files to be extracted for eventual
// translation.  It is primarily used for messages in thrown exceptions; see
// src/functexcept.cc.  We use __N because the more traditional _N is used
// for something else under certain OSes (see BADNAMES).
#define __N(msgid)     (msgid)