你能用数字开始一个类名吗？

问题描述

在 C ++ 中，是否可以使用数字启动类名称？例如，

 模板< class T> class 2DArray {
 
 public：
 // 1D ARRAY CLASS 
 class 1DArray {
 public：
 1DArray（）{Create（）; } 
 1DArray（iterator arr）：array1d_（arr）{} 
 explicit 1DArray（size_type cols，const T& t = T（））{Create（cols，t）; } 
 1DArray（const 1DArray& arr）{Create（arr.begin（），arr.end（））; } 
 1DArray& operator =（const 2DArray&）; 
〜1DArray（）{Uncreate（）; } 
 
 T& operator []（size_type n）{
 return array1d_ [n]; 
} 
 const T& operator []（size_type n）const {
 return array1d_ [n]; 
} 
} 
  

解决方案

中的标识符名称是：

1. 不能以数字开头


2. 可以由字母，数字，下划线，通用字符名称和实现定义的字符组成


3. a 。

在它说：

在 C ++ 的这也适用于因为这样的显示。

---

脚注

• 1。允许的通用字符

允许的通用字符包含在 / code>：




In C++, is it possible to start a class name with a digit? For example,

template <class T> class 2DArray {

public:
    // 1D ARRAY CLASS
    class 1DArray {
    public:
        1DArray() { Create(); }
        1DArray(iterator arr) : array1d_(arr) { }
        explicit 1DArray(size_type cols, const T& t = T()) { Create(cols, t); }
        1DArray(const 1DArray& arr) { Create(arr.begin(), arr.end()); }
        1DArray& operator=(const 2DArray&);
        ~1DArray() { Uncreate(); }

        T& operator[](size_type n) {
            return array1d_[n];
        }
        const T& operator[](size_type n) const {
            return array1d_[n];
        }
}

解决方案

Rules for identifier names in C++ are:

1. It can not start with a number
2. Can be composed of letters, numbers, underscore, universal character names and implementation defined characters
3. Can not be a keyword.

The sections in the C++ draft standard that cover this are 2.11 Identifiers which includes the following grammar:

identifier:
  identifier-nondigit            <- Can only start with a non-digit
  identifier identifier-nondigit <- Next two rules allows for subsequent
  identifier digit               <-  characters to be those outlined in 2 above
identifier-nondigit:
  nondigit                       <- a-z, A-Z and _
  universal-character-name
  other implementation-defined characters
[...]

and 2.12 Keywords explains all the identifier reserved for use as keywords.

Finally, the following names are also reserved:

1. Names that contain a double underscore __, or start with either an underscore followed by an uppercase letter (like _Apple) in any scope,
2. Names that start with an underscore in the global namespace (like _apple in the global namespace) are reserved.

The section that covers this in the draft standard is 17.6.4.3.2. We can find a rationale for why these are reserved from Rationale for International Standard—Programming Languages—C which says:

In C++ this also applies to name mangling as this example shows.

---

Footnotes

• 1. Allowed universal characters

The universal characters that are allowed is covered in Annex E.1:

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