How can I tell if a time was yesterday?

Hi,

Given a time I want to know if it is today or yesterday, (on the
server).

I cannot use time difference because if I log the time and it is 23:59
and I check again at 24:01 then the earlier time is, in fact,
yesterday.

so given time $a and time $b how can I calculate if $a is the day
before $b?

Thanks

FFMG


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FFMG escribió:
> Given a time I want to know if it is today or yesterday, (on the
> server).

function is_yesterday($timestamp){ // NOT TESTED
$start = mktime(0, 0, 0,
date('n', time()), date('j', time()), date('Y', time()));
$end = mktime(0, 0, 0,
date('n', time()), date('j', time()), date('Y', time()));

return ($timestamp>=$start) && ($timestamp<$end)
}


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On Wed, 15 Aug 2007 11:57:38 +0200, FFMG <FFMG.2vcq3z@no-mx.httppoint.com>
wrote:
> Given a time I want to know if it is today or yesterday, (on the
> server).
>
> I cannot use time difference because if I log the time and it is 23:59
> and I check again at 24:01 then the earlier time is, in fact,
> yesterday.
>
> so given time $a and time $b how can I calculate if $a is the day
> before $b?


What format is your time in? 24:01 is highly unusual to use. If you got
real timestamps, you can create & compare any timestamp using one of the
date formatting functions.

function is_today($timestamp){
return date('d',$timestamp) == date('d');
}
--
Rik Wasmus

On 15.08.2007 11:57 FFMG wrote:
> Hi,
>
> Given a time I want to know if it is today or yesterday, (on the
> server).
>
> I cannot use time difference because if I log the time and it is 23:59
> and I check again at 24:01 then the earlier time is, in fact,
> yesterday.
>
> so given time $a and time $b how can I calculate if $a is the day
> before $b?
>

if(unixtojd($b) - unixtojd($a) == 1)

http://www.php.net/manual/en/function.unixtojd.php

if the dates are in Mysql you'd be better off with TO_DAYS()


--
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php done right ;) http://code.google.com/p/pihipi

On Wed, 15 Aug 2007 12:23:52 +0200, gosha bine <stereofrog@gmail.com>
wrote:

> On 15.08.2007 11:57 FFMG wrote:
>> Hi, Given a time I want to know if it is today or yesterday, (on the
>> server).
>> I cannot use time difference because if I log the time and it is 23:59
>> and I check again at 24:01 then the earlier time is, in fact,
>> yesterday.
>> so given time $a and time $b how can I calculate if $a is the day
>> before $b?
>>
>
> if(unixtojd($b) - unixtojd($a) == 1)
>
> http://www.php.net/manual/en/function.unixtojd.php


Erm, Julian days start at noon?
--
Rik Wasmus

On 15.08.2007 12:26 Rik wrote:
> On Wed, 15 Aug 2007 12:23:52 +0200, gosha bine <stereofrog@gmail.com>
> wrote:
>
>> On 15.08.2007 11:57 FFMG wrote:
>>> Hi, Given a time I want to know if it is today or yesterday, (on the
>>> server).
>>> I cannot use time difference because if I log the time and it is 23:59
>>> and I check again at 24:01 then the earlier time is, in fact,
>>> yesterday.
>>> so given time $a and time $b how can I calculate if $a is the day
>>> before $b?
>>>
>>
>> if(unixtojd($b) - unixtojd($a) == 1)
>>
>> http://www.php.net/manual/en/function.unixtojd.php
>
>
> Erm, Julian days start at noon?

Don't trust every comment you see in the manual. ;)



--
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makrell ~ http://www.tagarga.com/blok/makrell
php done right ;) http://code.google.com/p/pihipi

On Wed, 15 Aug 2007 12:41:05 +0200, gosha bine <stereofrog@gmail.com>
wrote:

> On 15.08.2007 12:26 Rik wrote:
>> On Wed, 15 Aug 2007 12:23:52 +0200, gosha bine <stereofrog@gmail.com>
>> wrote:
>>
>>> On 15.08.2007 11:57 FFMG wrote:
>>>> Hi, Given a time I want to know if it is today or yesterday, (on the
>>>> server).
>>>> I cannot use time difference because if I log the time and it is
>>>> 23:59
>>>> and I check again at 24:01 then the earlier time is, in fact,
>>>> yesterday.
>>>> so given time $a and time $b how can I calculate if $a is the day
>>>> before $b?
>>>>
>>>
>>> if(unixtojd($b) - unixtojd($a) == 1)
>>>
>>> http://www.php.net/manual/en/function.unixtojd.php
>> Erm, Julian days start at noon?
>
> Don't trust every comment you see in the manual. ;)

Haven't examined the function, but I did see that comment yeah, and
wikipedia (well, another source of blatant lies sometimes, but hey) states:

<http://en.wikipedia.org/wiki/Julian_day>

The Julian day or Julian day number (JDN) is the integer number of days
that have elapsed since the initial epoch defined as noon Universal Time
(UT) Monday, January 1, 4713 BC in the proleptic Julian calendar [1]. That
noon-to-noon day is counted as Julian day 0. Thus the multiples of 7 are
Mondays. Negative values can also be used, although those predate all
recorded history.

Now at 00:20, Friday August 10, 2007 (UTC) the JDN is 2454322. The
remainder of this value divided by 7 is 3, an integer expression for the
day of the week with 0 representing Monday.

The Julian date (JD) is a continuous count of days and fractions elapsed
since the same initial epoch. Currently the JD is 2454322.51389. The
integral part (its floor) gives the Julian day number. The fractional part
gives the time of day since noon UT as a decimal fraction of one day or
fractional day, with 0.5 representing midnight UT. Typically, a 64-bit
floating point (double precision) variable can represent an epoch
expressed as a Julian date to about 1 millisecond precision.

Which led me to assume it to be true.

Then again, the manual points at
<http://www.hermetic.ch/cal_stud/jdn.htm>, which states there are several
posibilities to start the day... If you say the PHP function takes
midnight, I believe you :-)
--
Rik Wasmus

Rik;87140 Wrote:
> On Wed, 15 Aug 2007 11:57:38 +0200, FFMG
> <FFMG.2vcq3z@no-mx.httppoint.com>
> wrote:
> > Given a time I want to know if it is today or yesterday, (on the
> > server).
> >
> > I cannot use time difference because if I log the time and it is
> 23:59
> > and I check again at 24:01 then the earlier time is, in fact,
> > yesterday.
> >
> > so given time $a and time $b how can I calculate if $a is the day
> > before $b?
>
>
> What format is your time in? 24:01 is highly unusual to use. If you got
>
> real timestamps, you can create & compare any timestamp using one of
> the
> date formatting functions.
>
> function is_today($timestamp){
> return date('d',$timestamp) == date('d');
> }
> --
> Rik Wasmus

Sorry you are right, I was trying to illustrate my point.

I am using unix timestamp.

FFMG


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On 15.08.2007 12:54 Rik wrote:
> On Wed, 15 Aug 2007 12:41:05 +0200, gosha bine <stereofrog@gmail.com>
> wrote:
>
>> On 15.08.2007 12:26 Rik wrote:
>>> On Wed, 15 Aug 2007 12:23:52 +0200, gosha bine <stereofrog@gmail.com>
>>> wrote:
>>>
>>>> On 15.08.2007 11:57 FFMG wrote:
>>>>> Hi, Given a time I want to know if it is today or yesterday, (on the
>>>>> server).
>>>>> I cannot use time difference because if I log the time and it is
>>>>> 23:59
>>>>> and I check again at 24:01 then the earlier time is, in fact,
>>>>> yesterday.
>>>>> so given time $a and time $b how can I calculate if $a is the day
>>>>> before $b?
>>>>>
>>>>
>>>> if(unixtojd($b) - unixtojd($a) == 1)
>>>>
>>>> http://www.php.net/manual/en/function.unixtojd.php
>>> Erm, Julian days start at noon?
>>
>> Don't trust every comment you see in the manual. ;)
>
> Haven't examined the function, but I did see that comment yeah, and
> wikipedia (well, another source of blatant lies sometimes, but hey) states:
>
> <http://en.wikipedia.org/wiki/Julian_day>
> [quote] skipped
>
> Which led me to assume it to be true.
>
> Then again, the manual points at
> <http://www.hermetic.ch/cal_stud/jdn.htm>, which states there are
> several posibilities to start the day... If you say the PHP function
> takes midnight, I believe you :-)

php implementation is not that clever. It just pulls the date (year,
month, day) out of the timestamp[*] and calculates jd for this date.
It's completely unaware of times.
[*] Of course, the result of conversion depends on the local time
settings i.e. timezone and daylight saving state.



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makrell ~ http://www.tagarga.com/blok/makrell
php done right ;) http://code.google.com/p/pihipi

Rik wrote:

> function is_today($timestamp){
> return date('d',$timestamp) == date('d');
> }

The following will return TRUE:

is_today(strtotime('15 Feb 1986'));

Better would be:

function is_today ($ts)
{ return date('Ymd',$ts)==date('Ymd'); }

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