cppdraft_translate/cppdraft/lex/name.md

[lex.name]

5 Lexical conventions [lex]

5.11 Identifiers [lex.name]

identifier:
identifier-start
identifier identifier-continue

identifier-start:
nondigit
an element of the translation character set with the Unicode property XID_Start

identifier-continue:
digit
nondigit
an element of the translation character set with the Unicode property XID_Continue

nondigit: one of
a b c d e f g h i j k l m
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z _

digit: one of
0 1 2 3 4 5 6 7 8 9

1

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[Note 1:

The character properties XID_Start and XID_Continue are described by UAX #44 of the Unicode Standard.13

— end note]

The program is ill-formed if an identifier does not conform to Normalization Form C as specified in the Unicode Standard.

[Note 2:

Identifiers are case-sensitive.

— end note]

[Note 3:

[uaxid] compares the requirements of UAX #31 of the Unicode Standard with the C++ rules for identifiers.

— end note]

[Note 4:

In translation phase 4,identifier also includes those preprocessing-tokens ([lex.pptoken]) differentiated as keywords ([lex.key]) in the later translation phase 7 ([lex.token]).

— end note]

2

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The identifiers in Table 4 have a special meaning when appearing in a certain context.

When referred to in the grammar, these identifiers are used explicitly rather than using the identifier grammar production.

Unless otherwise specified, any ambiguity as to whether a givenidentifier has a special meaning is resolved to interpret the token as a regular identifier.

Table 4 — Identifiers with special meaning [tab:lex.name.special]

🔗 final	import	post	replaceable_if_eligible
🔗 override	module	pre	trivially_relocatable_if_eligible

3

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In addition, some identifiers appearing as a token or preprocessing-token are reserved for use by C++ implementations and shall not be used otherwise; no diagnostic is required.

• (3.1)

  Each identifier that contains a double underscore__or begins with an underscore followed by an uppercase letter, other than those specified in this document (for example, __cplusplus ([cpp.predefined])),is reserved to the implementation for any use.

• (3.2)

  Each identifier that begins with an underscore isreserved to the implementation for use as a name in the global namespace.

13)13)

On systems in which linkers cannot accept extended characters, an encoding of the universal-character-name can be used in forming valid external identifiers.

For example, some otherwise unused character or sequence of characters can be used to encode the\u in a universal-character-name.

Extended characters can produce a long external identifier, but C++ does not place a translation limit on significant characters for external identifiers.