Every use of colon (":") in C

Question

I'm curious about every context in which a colon (the ":" character) is a valid syntactic element (outside of a string/character literal, comment, etc) in a C program.

I tried searching C99 spec, but ":" matches every single page and "colon" doesn't find every usage. Similarly, by looking through toy C parsers (and I understand that lex/yacc aren't capable of parsing C) I only seem to find partial results.

These are the scenarios that I know use a colon:

• Conditional operator
• Bit field
• Labels

Are there any other language features in C that use a colon?

Answer 1

The C standard (N1570) defines digraphs:

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.

As a side note, C++ standard elaborates on the term:

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”.

According to 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.