On Thursday, 6 March 2025 14:29:34 Pacific Standard Time Howard Hinnant via
Std-Proposals wrote:
> I consider it a given that the macros C++ inherits from C: __DATE__ and
> __TIME__ are not intrinsically evil nor dangerous to use.

I disagree: they are evil to use. We have -Wdate-time for a reason.
‘-Wdate-time’
     Warn when macros ‘__TIME__’, ‘__DATE__’ or ‘__TIMESTAMP__’ are
     encountered as they might prevent bit-wise-identical reproducible
     compilations.

Compilers today can be told to fake the time too, so builds are reproducible.
So those macros aren't actually the current date and time, but instead are
some transformation from an environment variable configurable by the user.

If Nik's proposal is adopted, then the time std::chrono::system_clock::now()
returns will also be the same fake time. Software cannot depend on the number
being different between any two builds. In fact, a compliant compiler can
always return the same, fixed timestamp of any date, in the past or future,
like for example the date of the first release of the compiler.

So please don't depend on the time. If you need a seed of some sort, just pass
it from your buildsystem in a macro (either in the command-line or writing to
a seed file).

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Principal Engineer - Intel DCAI Platform & System Engineering