2 Lexical conventions [lex]

2.6 Alternative tokens [lex.digraph]

1

Alternative token representations are provided for some operators and punctuators.16

2

In all respects of the language, each alternative token behaves the same, respectively, as its primary token, except for its spelling.17 The set of alternative tokens is defined in Table [tab:alternative.tokens].

Table 2 — Alternative tokens
Alternative Primary Alternative Primary Alternative Primary
<% { and && and_eq &=
%> } bitor | or_eq |=
<: [ or || xor_eq ^=
:> ] xor ^ not !
%: # compl ~ not_eq !=
%:%: ## bitand &

16)

These include “digraphs” and additional reserved words. 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”.

17)

Thus the “stringized” values ([cpp.stringize]) of [ and <: will be different, maintaining the source spelling, but the tokens can otherwise be freely interchanged.