c - 宏名称的有效字符是什么？

Question

C 风格的宏名称是否遵循与标识符相同的命名规则？编译器升级后，它现在对遗留应用程序发出此警告:

warning #3649-D: white space is required between the macro name "CHAR_" and its replacement text
  #define         CHAR_&        38

这行代码定义了一个 & 符号的 ASCII 值常量。

#define   DOL_SN        36
#define   PERCENT       37
#define   CHAR_&        38
#define   RT_SING       39
#define   LF_PAR        40

我假设这个定义(据我所知，实际上没有被任何代码引用)是错误的，应该更改为类似“CHAR_AMPERSAND”的定义？

Answer 1

宏名称只能由字母数字字符和下划线组成，即 'a-z'、'A-Z'、'0-9' 和 '_'，第一个字符不能是数字。一些预处理器也允许美元符号字符 '$'，但你不应该使用它；不幸的是，我无法引用 C 标准，因为我没有它的副本。

来自GCC documentation :

Preprocessing tokens fall into five broad classes: identifiers, preprocessing numbers, string literals, punctuators, and other. An identifier is the same as an identifier in C: any sequence of letters, digits, or underscores, which begins with a letter or underscore. Keywords of C have no significance to the preprocessor; they are ordinary identifiers. You can define a macro whose name is a keyword, for instance. The only identifier which can be considered a preprocessing keyword is defined. See Defined.

This is mostly true of other languages which use the C preprocessor. However, a few of the keywords of C++ are significant even in the preprocessor. See C++ Named Operators.

In the 1999 C standard, identifiers may contain letters which are not part of the “basic source character set”, at the implementation's discretion (such as accented Latin letters, Greek letters, or Chinese ideograms). This may be done with an extended character set, or the '\u' and '\U' escape sequences. The implementation of this feature in GCC is experimental; such characters are only accepted in the '\u' and '\U' forms and only if -fextended-identifiers is used.

As an extension, GCC treats '$' as a letter. This is for compatibility with some systems, such as VMS, where '$' is commonly used in system-defined function and object names. '$' is not a letter in strictly conforming mode, or if you specify the -$ option. See Invocation.