CODEWITHSUNDEEP
clanguage-lawyerc99
ashastral
ashastral

Reputation: 2848

Does C99 permit universal character names in identifiers?

From §6.4.2 of the WG14/N1124 draft of the C99 spec, "Identifiers":

identifier:  
       identifier-nondigit  
       identifier identifier-nondigit  
       identifier digit

identifier-nondigit:  
       nondigit  
       universal-character-name  
       other implementation-defined characters

And §6.4.3, "Universal character names":

universal-character-name:
       \u hex-quad
       \U hex-quad hex-quad

This seems to suggest that an identifier like foo\u00AAbar is valid according to the grammar. I can't find anything in the semantics that would suggest otherwise. Yet GCC rejects such an identifier without even trying to parse it:

<stdin>:2: error: stray ‘\’ in program
<stdin>:2: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘u00AAbar’
<stdin>:2: error: ‘u00AAbar’ undeclared (first use in this function)

Is this an oversight in GCC, the C99 standard, or my reasoning?

Upvotes: 3

Views: 721

Answers (1)

user743382
user743382

Reputation:

None of those three. It's simply a long-standing unimplemented (or rather, only partially implemented) feature. It's recently been completed, and will be available in GCC 5. Prior to that version, you can use the -fextended-identifiers command-line option, but there are some cases that it got wrong that led to it not being enabled by default.

You can see this listed on Status of C99 features in GCC.

Upvotes: 7

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