Java date to C++

Hello,

I need to send a Java date (milliseconds since the epoch 1970-01-01
00:00:00.000 GMT) through a socket to a C++ app and reconstruct exactly the
same date in the C++ app as in the Java app.

The date (actually the milliseconds since the epoch) is splitted in 8 bytes
and sent through the socket.

How can I recalculate the date in c++? Are there methods / classes for this
purpose in c++? And if not: how is the amount of milliseconds in Java
precisely calculated?

greetings,

Mike

[Roedy Green]

On Tue, 18 Oct 2005 01:14:41 +0200, <Mike> wrote or quoted :

How can I recalculate the date in c++?

There is nothing to calculate. The only problem you might have is
endianness. To write a little-endian long see nio or
http://mindprod.com/products1.html#LEDATASTREAM

Perhaps your problem is reconstructing a long from 8 bytes in C?
Look at how LeDataInputStre am does it in Java. The C code would be
very similar.

--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

[Victor Bazarov]

Mike wrote:

I need to send a Java date (milliseconds since the epoch 1970-01-01
00:00:00.000 GMT) through a socket to a C++ app and reconstruct
exactly the same date in the C++ app as in the Java app.

The date (actually the milliseconds since the epoch) is splitted in 8
bytes and sent through the socket.

How can I recalculate the date in c++? Are there methods / classes
for this purpose in c++?
Not in the Standard C++. But if leap seconds are not very important,
you should simply assume 1000 ms per sec, 60 sec per min, 60 mins per
hr, 24 hrs per day, 365 (or 366) days per year, I recon. Once you
have the GMT date, you can use 'mktime' and 'localtime' functions to
reconstruct the local time.
And if not: how is the amount of
milliseconds in Java precisely calculated?

Shouldn't you ask this in a Java newsgroup?

V

[Victor Bazarov]

Roedy Green wrote:

On Tue, 18 Oct 2005 01:14:41 +0200, <Mike> wrote or quoted :

How can I recalculate the date in c++? There is nothing to calculate. The only problem you might have is
endianness. To write a little-endian long see nio or
http://mindprod.com/products1.html#LEDATASTREAM

Perhaps your problem is reconstructing a long from 8 bytes in C?

(a) It's C++.
(b) 'long' is often only 4 bytes, it would be impossible to reconstruct
it in that case, don't you think?
Look at how LeDataInputStre am does it in Java. The C code would be
very similar.

It's C++.

V

[red floyd]

Victor Bazarov wrote:

Not in the Standard C++. But if leap seconds are not very important,
you should simply assume 1000 ms per sec, 60 sec per min, 60 mins per
hr, 24 hrs per day, 365 (or 366) days per year, I recon. Once you
have the GMT date, you can use 'mktime' and 'localtime' functions to
reconstruct the local time.

What's wrong with using some form of multi-precision integer class,
dividing by 1000, checking for overflow, and using the result as a
time_t? localtime() and gmtime() use secnods since epoch UTC.

[Mike Wahler]

"red floyd" <no*****@here.d ude> wrote in message
news:7u******** *********@newss vr25.news.prodi gy.net...

Victor Bazarov wrote:

Not in the Standard C++. But if leap seconds are not very important,
you should simply assume 1000 ms per sec, 60 sec per min, 60 mins per
hr, 24 hrs per day, 365 (or 366) days per year, I recon. Once you
have the GMT date, you can use 'mktime' and 'localtime' functions to
reconstruct the local time.

What's wrong with using some form of multi-precision integer class,
dividing by 1000, checking for overflow, and using the result as a time_t?
localtime() and gmtime() use secnods since epoch UTC.

I don't believe there's any requirement that 'time_t'
be an integer type, or that there is a conversion from
an integer type to a 'time_t'.

-Mike

[Victor Bazarov]

Mike Wahler wrote:

"red floyd" <no*****@here.d ude> wrote in message
news:7u******** *********@newss vr25.news.prodi gy.net...

Victor Bazarov wrote:

Not in the Standard C++. But if leap seconds are not very
important, you should simply assume 1000 ms per sec, 60 sec per
min, 60 mins per hr, 24 hrs per day, 365 (or 366) days per year, I
recon. Once you have the GMT date, you can use 'mktime' and
'localtime' functions to reconstruct the local time.

What's wrong with using some form of multi-precision integer class,
dividing by 1000, checking for overflow, and using the result as a
time_t? localtime() and gmtime() use secnods since epoch UTC.

I don't believe there's any requirement that 'time_t'
be an integer type, or that there is a conversion from
an integer type to a 'time_t'.

That's true. There is no requirement that 'time_t' is in any way
related to January 1st, 1970, either.

V

[Branimir Maksimovic]

<Mike> wrote in message news:43******** *************** @news.xs4all.nl ...

Hello,

I need to send a Java date (milliseconds since the epoch 1970-01-01
00:00:00.000 GMT) through a socket to a C++ app and reconstruct exactly
the same date in the C++ app as in the Java app.

The date (actually the milliseconds since the epoch) is splitted in 8
bytes and sent through the socket.
Is date big endian or little endian?signed or unsigned?
Is it send as two consecutive 4 byte integers or single one?
Do you use any standard api CDR/XDR for example?

How can I recalculate the date in c++? Are there methods / classes for
this purpose in c++?

If you know the details calculation is not a problem :)

Greetings, Bane.

[jfbriere]

No need for big calculations.
There are standard C functions that deal with it.
Take a look at:
http://www.delorie.com/gnu/docs/glibc/libc_435.html

You have to be careful with OS specifics:

1- Endianness: be sure that the 8 bytes from java (allways big endian)
will be
assign correctly in the c++ part.

2- The standard C functions use time_t, which is typically define as a
long (you must verify it in time.h -> sys/types.h) which is typically
32bits (depending on systems) which 4 bytes and NOT 8 bytes.

3- java.util.Date. getTime() returns a long which is the number of
milliseconds since the epoch.
On the other hand, the standard C functions use time_t which represents
the number of seconds since the epoch.
Epochs are the same in both cases.

Good luck!

[Pep]

<Mike> wrote:

Hello,

I need to send a Java date (milliseconds since the epoch 1970-01-01
00:00:00.000 GMT) through a socket to a C++ app and reconstruct exactly
the same date in the C++ app as in the Java app.

The date (actually the milliseconds since the epoch) is splitted in 8
bytes and sent through the socket.

How can I recalculate the date in c++? Are there methods / classes for
this purpose in c++? And if not: how is the amount of milliseconds in Java
precisely calculated?

greetings,

Mike

Use the getTimeInMillis method of the Calendar class to get the UTC which is
a long int, then send that to the C++ program.

In C++ use localtime to convert to a tm struct to be able to mess with the
individual time components.

Cheers,
Pep.