C ++ 11允许标识符中的美元符号吗？ [英] Does C++11 allow dollar signs in identifiers?

问题描述

C ++ 03中的标识符中是否允许使用美元符号？ 涵盖了C ++ 03中不允许使用标识符中的美元符号。 GCC将其作为 C扩展提供，并在C ++中正确提供诊断03模式。但是，在C ++ 11中， int $ = 0 将在没有警告的情况下编译。

Are dollar-signs allowed in identifiers in C++03? covers that dollar signs in identifiers are not allowed in C++03. GCC provides it as a C extension and properly gives a diagnostic in C++03 mode. However, in C++11, int $ = 0 will compile without warning.

http://stackoverflow.com/a/16055409/3920237\">answer 原因可能允许使用 $ ，因为实施定义的标识符不需要诊断：

This answer reasons that $ may be allowed because no diagnostic is required for implementation defined identifiers:

这里的答案是可能：根据§2.11
可以包含数字和 identifier-nondigits ，从后者的一个
开始。 identifier-nondigits 是通常的 az ， AZ 和
下划线除了自C ++ 11它们包括
通用字符名（例如 \\\뺯 ， \\UC0FFEE32 ），和其他实现定义的字符。因此，如果在标识符中使用 $ ，那么它是实现定义的
。 VC10和up支持，
也许是较早的版本，太。它甚至支持像
こんばんわ的标识符。

The answer here is "Maybe": According to §2.11, identifiers may consist of digits and identifier-nondigits, starting with one of the latter. identifier-nondigits are the usual a-z, A-Z and underscore, in addition since C++11 they include universal-character-names (e.g. \uBEAF, \UC0FFEE32), and other implementation-defined characters. So it is implementation defined if using $ in an identifier is allowed. VC10 and up supports that, maybe earlier versions, too. It even supports identifiers like こんばんわ.

但：我不会使用它们。使标识符尽可能可读和便携。 $ 是实现定义的，因此不是
可移植。

But: I wouldn't use them. Make identifiers as readable and portable as possible. $ is implementation defined and thus not portable.

语言也存在于C ++ 03标准中，所以我不认为这是一个非常有说服力的论据。

This language is present in the C++03 standard as well, so I don't find this to be a very convincing argument.

§2.10/ 2

此外，一些标识符保留供C ++
实现和标准库（17.6.4.3.2）使用，并且不应
否则使用;

In addition, some identifiers are reserved for use by C ++ implementations and standard libraries (17.6.4.3.2) and shall not be used otherwise; no diagnostic is required.

标准中的更改允许 $ 用作标识符名称？

What change in the standard allows $ to be used as an identifier name?

推荐答案

这是实现定义的行为， $ 不包括在标识符的语法中。 C ++ 11 中标识符名称的规则是：

This is implementation defined behavior, $ is not included in grammar for identifiers. The rules for identifier names in C++11 are:

1. 不能以数字开头
2. 
   
3. 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


4. 不能是关键字

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

允许使用实现定义的字符，许多编译器支持作为扩展名，包括 gcc ， clang ， Visual Studio ，并在 comment 显然是 DEC C ++编译器。

Implementation-defined characters are allowed and many compilers support as an extension, including gcc, clang, Visual Studio and as noted in a comment apparently DEC C++ compilers.

语法包含在草稿C ++标准部分 2.11 标签，I添加了以< - 开头的附加注释：

The grammar is covered in the draft C++ standard section 2.11 Indentifier, I added additional notes starting with <-:

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
[...]

如果我们使用 clang code> -pedantic-errors 标志它不会编译：

If we compile this code using clang with the -pedantic-errors flag it will not compile:

int $ = 0

并产生以下错误：

error: '$' in identifier [-Werror,-Wdollar-in-identifier-extension]
int $ = 0;
    ^

这篇关于C ++ 11允许标识符中的美元符号吗？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！