Converts this TimeOfDay to a string with the format HHMMSS. If writer is set, the resulting string will be written directly to it.
A string when not using an output range; void otherwise.
assert(TimeOfDay(0, 0, 0).toISOString() == "000000"); assert(TimeOfDay(12, 30, 33).toISOString() == "123033");
See Implementation
Converts this TimeOfDay to a string with the format HHMMSS. If writer is set, the resulting string will be written directly to it.