Hi group,

I have been using strtotime a lot in my code.
I wonder if I made a mistake in my thinking. :-/
Here follows a stripped down example.

consider some dates:
$date1 = "2008-02-23";
$date2 = "2008-02-23";
(They are the same)

Suppose I need to know if date1 is smaller/equal or bigger than date2.
I often used code like:
$UTSdate1 = strtotime($date1);
$UTSdate2 = strtotime($date2);

if ($UTSdate1 <= $UTSdate2){
// date1 before or equal to date2
} else {
// date1 after date2
}

Good, not?

I think not after rereading the manual:

FROM: http://nl2.php.net/manual/en/function.strtotime.php

int strtotime ( string $time [, int $now ] )

The function expects to be given a string containing a US English date
format and will try to parse that format into a Unix timestamp (the
number of seconds since January 1 1970 00:00:00 GMT), relative to the
timestamp given in now , or the current time if now is not supplied.

The part "relative to the timestamp given in now" got me confused.

My question: Since the strtotime() is calculating 2 times the Unix Time
Stamp, do I risk that during execution of my script the second is
increased between the first call to strtotime() and the second, thus
making my above approach invalid?

Would this be better?
$UTSnow = time();
$UTSdate1 = strtotime($date1,$now);
$UTSdate2 = strtotime($date2,$now);

Should I change my code according to the second approach (using $UTSnow)?
I know chances of ticking a second are small in such a small piece of
code, but I don't want to deliver code that 'works most of the time'.

Thanks for any insights.

Regards,
Erwin Moller

Erwin Moller schreef:

<snip typo correction)

> Would this be better?
> $UTSnow = time();
> $UTSdate1 = strtotime($date1,$now);
> $UTSdate2 = strtotime($date2,$now);
>

should read of course:
$UTSnow = time();
$UTSdate1 = strtotime($date1,$UTSnow);
$UTSdate2 = strtotime($date2,$UTSnow);

Erwin

On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
<Since_humans_read_this_I_am_spammed_too_much@spam yourself.com> wrote:

> Erwin Moller schreef:
>
> <snip typo correction)
>
>> Would this be better?
>> $UTSnow = time();
>> $UTSdate1 = strtotime($date1,$now);
>> $UTSdate2 = strtotime($date2,$now);
>>
>
> should read of course:
> $UTSnow = time();
> $UTSdate1 = strtotime($date1,$UTSnow);
> $UTSdate2 = strtotime($date2,$UTSnow);

Giving an explicit date will render the 'relative' part useless:
<?php
date_default_timezone_set('Europe/Amsterdam');
$date = "2008-02-23";
$UTSdate1 = strtotime($date);
sleep(2);
$UTSdate2 = strtotime($date);
var_dump($UTSdate1,$UTSdate2);
?>
Output:
int(1203721200)
int(1203721200)

However, giving a relative date, they can differ:
<?php
date_default_timezone_set('Europe/Amsterdam');
$date = "-2 hours";
//without supplying relative to what:
$UTSdate1 = strtotime($date);
sleep(2);
$UTSdate2 = strtotime($date);
var_dump($UTSdate1,$UTSdate2);
//with supplying a previously created timestamp:
$now = time();
$UTSdate1 = strtotime($date,$now);
sleep(2);
$UTSdate2 = strtotime($date,$now);
var_dump($UTSdate1,$UTSdate2);
?>
int(1209020255)
int(1209020257)
int(1209020257)
int(1209020257)

So you only have a problem with 'relative' datestrings ( +/- N hours,
'last Saturday', etc.). Specific datestrings are not relative to anything
in this context, so will yield the same output.
--
Rik Wasmus

On Thu, 24 Apr 2008 11:00:45 +0200, Rik Wasmus
<luiheidsgoeroe@hotmail.com> wrote:

> On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
> <Since_humans_read_this_I_am_spammed_too_much@spam yourself.com> wrote:
>
>> Erwin Moller schreef:
>>
>> <snip typo correction)
>>
>>> Would this be better?
>>> $UTSnow = time();
>>> $UTSdate1 = strtotime($date1,$now);
>>> $UTSdate2 = strtotime($date2,$now);
>>>
>>
>> should read of course:
>> $UTSnow = time();
>> $UTSdate1 = strtotime($date1,$UTSnow);
>> $UTSdate2 = strtotime($date2,$UTSnow);
>
> Giving an explicit date will render the 'relative' part useless:
> <?php
> date_default_timezone_set('Europe/Amsterdam');
> $date = "2008-02-23";
> $UTSdate1 = strtotime($date);
> sleep(2);
> $UTSdate2 = strtotime($date);
> var_dump($UTSdate1,$UTSdate2);
> ?>
> Output:
> int(1203721200)
> int(1203721200)
>
> However, giving a relative date, they can differ:
> <?php
> date_default_timezone_set('Europe/Amsterdam');
> $date = "-2 hours";
> //without supplying relative to what:
> $UTSdate1 = strtotime($date);
> sleep(2);
> $UTSdate2 = strtotime($date);
> var_dump($UTSdate1,$UTSdate2);
> //with supplying a previously created timestamp:
> $now = time();
> $UTSdate1 = strtotime($date,$now);
> sleep(2);
> $UTSdate2 = strtotime($date,$now);
> var_dump($UTSdate1,$UTSdate2);
> ?>
> int(1209020255)
> int(1209020257)
> int(1209020257)
> int(1209020257)
>
> So you only have a problem with 'relative' datestrings ( +/- N hours,
> 'last Saturday', etc.). Specific datestrings are not relative to
> anything in this context, so will yield the same output.

And on a sidenote: depending on the circumstances, I usually compare
timestamps which have to match within a margin of error (kind of like
float comparisons):

if($date1 - $error < $date2 < $date1 + $error){
//equal enough for this comparison
} else {
//outside margin of error
}
--
Rik Wasmus

Rik Wasmus schreef:
> On Thu, 24 Apr 2008 11:00:45 +0200, Rik Wasmus
> <luiheidsgoeroe@hotmail.com> wrote:
>
>> On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
>> <Since_humans_read_this_I_am_spammed_too_much@spam yourself.com> wrote:
>>
>>> Erwin Moller schreef:
>>>
>>> <snip typo correction)
>>>
>>>> Would this be better?
>>>> $UTSnow = time();
>>>> $UTSdate1 = strtotime($date1,$now);
>>>> $UTSdate2 = strtotime($date2,$now);
>>>>
>>>
>>> should read of course:
>>> $UTSnow = time();
>>> $UTSdate1 = strtotime($date1,$UTSnow);
>>> $UTSdate2 = strtotime($date2,$UTSnow);
>>
>> Giving an explicit date will render the 'relative' part useless:
>> <?php
>> date_default_timezone_set('Europe/Amsterdam');
>> $date = "2008-02-23";
>> $UTSdate1 = strtotime($date);
>> sleep(2);
>> $UTSdate2 = strtotime($date);
>> var_dump($UTSdate1,$UTSdate2);
>> ?>
>> Output:
>> int(1203721200)
>> int(1203721200)
>>
>> However, giving a relative date, they can differ:
>> <?php
>> date_default_timezone_set('Europe/Amsterdam');
>> $date = "-2 hours";
>> //without supplying relative to what:
>> $UTSdate1 = strtotime($date);
>> sleep(2);
>> $UTSdate2 = strtotime($date);
>> var_dump($UTSdate1,$UTSdate2);
>> //with supplying a previously created timestamp:
>> $now = time();
>> $UTSdate1 = strtotime($date,$now);
>> sleep(2);
>> $UTSdate2 = strtotime($date,$now);
>> var_dump($UTSdate1,$UTSdate2);
>> ?>
>> int(1209020255)
>> int(1209020257)
>> int(1209020257)
>> int(1209020257)
>>
>> So you only have a problem with 'relative' datestrings ( +/- N hours,
>> 'last Saturday', etc.). Specific datestrings are not relative to
>> anything in this context, so will yield the same output.
>
> And on a sidenote: depending on the circumstances, I usually compare
> timestamps which have to match within a margin of error (kind of like
> float comparisons):
>
> if($date1 - $error < $date2 < $date1 + $error){
> //equal enough for this comparison
> } else {
> //outside margin of error
> }

Thanks a lot Rik.
Very clear explanation. :-)

My confusion was clearly based on my total misunderstanding of the
'relative to' part, which was about a passed string like '+5 hours'.

Confusion cleared up now, and I feel a bit stupid too for asking. ;-)

Regards,
Erwin Moller

On 24 Apr, 09:47, Erwin Moller
<Since_humans_read_this_I_am_spammed_too_m...@spam yourself.com> wrote:
> I think not after rereading the manual:
>
> FROM:http://nl2.php.net/manual/en/function.strtotime.php
>

> int strtotime ( string $time [, int $now ] )
>
> The function expects to be given a string containing a US English date
> format and will try to parse that format into a Unix timestamp (the
> number of seconds since January 1 1970 00:00:00 GMT), relative to the
> timestamp given in now , or the current time if now is not supplied.
>

Hi Erwin,
in another recent thread I mentioned that the statement "The function
expects to be given a string containing a US English date format" is
contradicted later in the same page.

Captain Paralytic schreef:
> On 24 Apr, 09:47, Erwin Moller
> <Since_humans_read_this_I_am_spammed_too_m...@spam yourself.com> wrote:
>> I think not after rereading the manual:
>>
>> FROM:http://nl2.php.net/manual/en/function.strtotime.php
>>

>> int strtotime ( string $time [, int $now ] )
>>
>> The function expects to be given a string containing a US English date
>> format and will try to parse that format into a Unix timestamp (the
>> number of seconds since January 1 1970 00:00:00 GMT), relative to the
>> timestamp given in now , or the current time if now is not supplied.
>>

> Hi Erwin,
> in another recent thread I mentioned that the statement "The function
> expects to be given a string containing a US English date format" is
> contradicted later in the same page.

Hi,

Yes, I can hardly say '+5 days' is an English date format.

Since we both get confused by this entry in the manual, I suggest
somebody rewrites it.
Or, of course, we both suck and should find another job than programming
PHP. ;-)
Anyway, Rik cleared up my misunderstanding of that relative part, and I
think I keep programming PHP.

Regards,
Erwin Moller

On Thu, 24 Apr 2008 11:55:08 +0200, Erwin Moller
<Since_humans_read_this_I_am_spammed_too_much@spam yourself.com> wrote:

> Captain Paralytic schreef:
>> On 24 Apr, 09:47, Erwin Moller
>> <Since_humans_read_this_I_am_spammed_too_m...@spam yourself.com> wrote:
>>> I think not after rereading the manual:
>>>
>>> FROM:http://nl2.php.net/manual/en/function.strtotime.php
>>>

>>> int strtotime ( string $time [, int $now ] )
>>>
>>> The function expects to be given a string containing a US English date
>>> format and will try to parse that format into a Unix timestamp (the
>>> number of seconds since January 1 1970 00:00:00 GMT), relative to the
>>> timestamp given in now , or the current time if now is not supplied.
>>>

>> Hi Erwin,
>> in another recent thread I mentioned that the statement "The function
>> expects to be given a string containing a US English date format" is
>> contradicted later in the same page.
>
> Yes, I can hardly say '+5 days' is an English date format.

Well, '+5 dagen' or '+5 jours' is not understood, so I'd say it's english,
allthough not a date format :P

> Since we both get confused by this entry in the manual, I suggest
> somebody rewrites it.
> Or, of course, we both suck and should find another job than programming
> PHP. ;-)
> Anyway, Rik cleared up my misunderstanding of that relative part, and I
> think I keep programming PHP.

The manual of strtotime can be confusing yes. When in doubt, I just test,
which leads me to believe i should just take it as 'strtotime will expect
a dd/dd[/dd[dd]] string to be in US format' (and for instance not
dd-dd-dddd):
echo strtotime('02-03-1980');//320799600, 1980-03-02
echo strtotime('02/03/1980');//318380400, 1980-02-03
echo strtotime('02-03');//unrecognized, 1970-01-01
echo strtotime('02/03');//US, 2008-02-03

Indeed not clear from the manual, just trial and error...
--
Rik Wasmus