我很好奇一个冒号(“：”字符)在C程序中是一个有效的句法元素(在字符串/字符文字,注释等之外).
我尝试搜索C99规范,但“：”匹配每一个页面,“冒号”没有找到每一个用法.同样的,通过玩具C parsers(我明白lex / yacc aren’t capable的解析C),我似乎只是找到部分结果.
这些是我知道使用冒号的场景：
>条件运算符
>位字段
>标签
C中是否有其他语言功能使用冒号？
C标准(N1570)定义了有向图：
6.4.6 Punctuators
….
3 In all aspects of the language,the six tokens
<: :> <% %> %: %:%:
behave,respectively,the same as the six tokens 79)
[ ] { } # ##
except for their spelling.80)
79) These tokens are sometimes called ‘‘digraphs’’.
80) Thus [ and <: behave differently when ‘‘stringized’’ (see 6.10.3.2),but can otherwise be freely interchanged.
作为附注,C标准阐述了以下术语：
The term “digraph” (token consisting of two characters) is not
perfectly descriptive,since one of the alternative preprocessing-tokens is %:%: and of course several primary tokens contain two
characters. Nonetheless,those alternative tokens that aren’t lexical keywords are colloquially known as “digraphs”.
根据Digraphs and trigraphs：
In 1994 a normative amendment to the C standard,included in C99,supplied digraphs as more readable alternatives to five of the trigraphs. ….
Unlike trigraphs,digraphs are handled during tokenization,and any digraph must always represent a full token by itself,or compose the token %:%: replacing the preprocessor concatenation token ##. If a digraph sequence occurs inside another token,for example a quoted string,or a character constant,it will not be replaced.
