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).
(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.)
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.