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Answer 1

+3 A:

Java's Date.getTime returns the number of milliseconds from the epoch, whereas the C++ code expects the number of seconds from the epoch, so you need to divide by 1000 then truncate:

int timestampAsInt = (int)(timestampAsLong / 1000);

Java has only a signed integer not unsigned, but this should work.

Mark Byers 2010-02-16 16:03:10

I tried this already - there is data loss and the resulting date is far in the future. Java for some reason fills out the whole 64-bit variable with a date.Example:Java - 1266336527340C++ - 1266336583C++ after casting from Java 3616142316 (back to the future :))

SyBer 2010-02-16 16:10:25

Looking at your examples, it appears that you need to divide by 1000 first. I guess Java stores milliseconds from the epoch, whereas a 32-bit type would have seconds from the epoch.

Mark Byers 2010-02-16 16:18:11

Updated my answer, and I've confirmed that if you use Date.getTime, you do indeed get the number of miiliseconds, not seconds which explains the factor 1000.

Mark Byers 2010-02-16 16:21:27

Duh - should have understood it myself! :)

SyBer 2010-02-16 16:44:54

Answer 2

+1 A:

long javaTime = someDate.getTime();
int cTime = (int)((javaTime + 500) / 1000);

I prefer rounding over truncation, but you will have to decide which is right for your business rules.

Frank Krueger 2010-02-16 16:47:54

Here you basically rounding up, right?

SyBer 2010-02-16 16:55:41

No, I'm rounding using the normal rules. 1.5 rounds to 2.0. 1.4 rounds to 1.0. The beauty of integer arithmetic.

Frank Krueger 2010-02-16 16:58:57

My bad - it rounded correctly indeed.

SyBer 2010-02-16 17:07:27

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64-bit unsigned to 32-bit signed

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