Are C++14 digit separators allowed in user defined literals?

Question

While clang compiles the following line, g++ 6.1 complains about the digit separator (see live example on Coliru):

auto time = 01'23s; 

Which compiler, if any, is correct according to the C++14 standard (N3796)?

Otherwise, is allowing digit separators (§2.14.2) just an implementation detail in the user-defined literals (§2.14.8) of the <chrono> library (§20.12.5.8)? IMHO it should be not, since these literals are defined on unsigned long long parameters.

I remember Howard Hinnant using 10'000s as an example during his CppCon 2016 talk "A <chrono> tutorial" (at about 42 minutes in his talk).

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(Please note, that I did not intend to code "1 minute and 23 seconds", which is only correct by accident, since the octal literal 0123 is 64 + 16 + 3 == 83. For that purpose I should write

auto time = 1min + 23s; 

but that possible misleading interpretation is not part of the question.)

Answer 1

If you look at the grammar, user-defined-integer-literal can be octal-literal ud-suffix, and octal-literal is defined as either 0 or octal-literal ’_opt octal-digit.

N4140 §2.14.8

user-defined-literal:

• user-defined-integer-literal
• [...]

user-defined-integer-literal:

• octal-literal ud-suffix
• [...]

​

N4140 §2.14.2

octal-literal:

• 0
• octal-literal ’_opt octal-digit

So 01'23s is a perfectly valid literal.

Answer 2

WLOG for decimal literals:

[lex.ext]:

user-defined-integer-literal:
    decimal-literal ud-suffix

[lex.icon]:

decimal-literal:
    nonzero-digit
    decimal-literal  ’_opt  digit

I.e. yes, digit separators are allowed in UDLs.