Accurately serializing and deserializing a SysTime in binary format

[Ecstatic Coder]

On Tuesday, 21 July 2020 at 11:01:20 UTC, drug wrote:
> On 7/20/20 10:04 PM, Ecstatic Coder wrote:
>> I'm currently implementing a small open source backup tool 
>> (dub), and therefore I need to accurately store the file 
>> modification SysTime in binary format, so that I can later 
>> load this SysTime from the snapshot file to compare it with 
>> the current file modification SysTime.
>> 
>> Having unfortunately not understood how to do this from the 
>> SysTime documentation, in despair, I've tried to directly 
>> serialize the 16 bytes of the SysTime value. This worked fine 
>> until I call the ".toISOString()" on the deserialized SysTime, 
>> which inevitably crashes the executable ;)
>
> That is probably a bug. I serialize SysTime as long by means 
> msgpack for exchanging between C++ client and D server and it 
> works pretty nice.
>
>> 
>> Anyway, that's not really want I intended to do, as in 
>> practice a "ulong" already has enough  resolution for that 
>> purpose.
>> 
>> So sorry for my ignorance, but I would definitely need some 
>> help on how to :
>> - convert a file modification SysTime to a serializable 
>> number, for instance the number of hectonanoseconds since 
>> 1/1/1970 in UTC;
>> - convert that number back into a SysTime that I can compare 
>> to the modification SysTime of the same file.
>> 
>> Eric

Ah thanks for telling me :)

The loaded byte array in the union type was indeed the same as 
the saved one, so I immediately thought it was crashing because 
of some hidden pointer for timezone or something which was then 
pointing to garbage at reloading, causing the crash of the 
".toISOString" call.