bad usage of strtotime?

[Erwin Moller]

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:
$UTSdate1 = strtotime($date 1);
$UTSdate2 = strtotime($date 2);

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();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$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]

Erwin Moller schreef:

<snip typo correction)

Would this be better?
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$now);

should read of course:
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$UTSnow);
$UTSdate2 = strtotime($date 2,$UTSnow);

Erwin

[Rik Wasmus]

On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
<Si************ *************** *************** @spamyourself.c omwrote:

Erwin Moller schreef:

<snip typo correction)

>Would this be better?
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$now);

should read of course:
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$UTSnow);
$UTSdate2 = strtotime($date 2,$UTSnow);

Giving an explicit date will render the 'relative' part useless:
<?php
date_default_ti mezone_set('Eur ope/Amsterdam');
$date = "2008-02-23";
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSda te1,$UTSdate2);
?>
Output:
int(1203721200)
int(1203721200)

However, giving a relative date, they can differ:
<?php
date_default_ti mezone_set('Eur ope/Amsterdam');
$date = "-2 hours";
//without supplying relative to what:
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSda te1,$UTSdate2);
//with supplying a previously created timestamp:
$now = time();
$UTSdate1 = strtotime($date ,$now);
sleep(2);
$UTSdate2 = strtotime($date ,$now);
var_dump($UTSda te1,$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

[Rik Wasmus]

On Thu, 24 Apr 2008 11:00:45 +0200, Rik Wasmus
<lu************ @hotmail.comwro te:

On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
<Si************ *************** *************** @spamyourself.c omwrote:

>Erwin Moller schreef:

<snip typo correction)

>>Would this be better?
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$now);

should read of course:
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$UTSnow);
$UTSdate2 = strtotime($date 2,$UTSnow);

Giving an explicit date will render the 'relative' part useless:
<?php
date_default_ti mezone_set('Eur ope/Amsterdam');
$date = "2008-02-23";
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSda te1,$UTSdate2);
?>
Output:
int(1203721200)
int(1203721200)

However, giving a relative date, they can differ:
<?php
date_default_ti mezone_set('Eur ope/Amsterdam');
$date = "-2 hours";
//without supplying relative to what:
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSda te1,$UTSdate2);
//with supplying a previously created timestamp:
$now = time();
$UTSdate1 = strtotime($date ,$now);
sleep(2);
$UTSdate2 = strtotime($date ,$now);
var_dump($UTSda te1,$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

[Erwin Moller]

Rik Wasmus schreef:

On Thu, 24 Apr 2008 11:00:45 +0200, Rik Wasmus
<lu************ @hotmail.comwro te:

>On Thu, 24 Apr 2008 10:49:41 +0200, Erwin Moller
<Si*********** *************** *************** *@spamyourself. comwrote:

>>Erwin Moller schreef:

<snip typo correction)

Would this be better?
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$now);
should read of course:
$UTSnow = time();
$UTSdate1 = strtotime($date 1,$UTSnow);
$UTSdate2 = strtotime($date 2,$UTSnow);

Giving an explicit date will render the 'relative' part useless:
<?php
date_default_t imezone_set('Eu rope/Amsterdam');
$date = "2008-02-23";
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSd ate1,$UTSdate2) ;
?>
Output:
int(1203721200 )
int(1203721200 )

However, giving a relative date, they can differ:
<?php
date_default_t imezone_set('Eu rope/Amsterdam');
$date = "-2 hours";
//without supplying relative to what:
$UTSdate1 = strtotime($date );
sleep(2);
$UTSdate2 = strtotime($date );
var_dump($UTSd ate1,$UTSdate2) ;
//with supplying a previously created timestamp:
$now = time();
$UTSdate1 = strtotime($date ,$now);
sleep(2);
$UTSdate2 = strtotime($date ,$now);
var_dump($UTSd ate1,$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 misunderstandin g 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

[Captain Paralytic]

On 24 Apr, 09:47, Erwin Moller
<Since_humans_r ead_this_I_am_s pammed_too_m... @spamyourself.c omwrote:

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.

[Erwin Moller]

Captain Paralytic schreef:

On 24 Apr, 09:47, Erwin Moller
<Since_humans_r ead_this_I_am_s pammed_too_m... @spamyourself.c omwrote:

>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 misunderstandin g of that relative part, and I
think I keep programming PHP.

Regards,
Erwin Moller

[Rik Wasmus]

On Thu, 24 Apr 2008 11:55:08 +0200, Erwin Moller
<Si************ *************** *************** @spamyourself.c omwrote:

Captain Paralytic schreef:

>On 24 Apr, 09:47, Erwin Moller
<Since_humans_ read_this_I_am_ spammed_too_m.. .@spamyourself. comwrote:

>>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 misunderstandin g 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

[=?iso-8859-1?Q?Kim_Andr=E9_Aker=F8?=]

Erwin Moller wrote:

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:
$UTSdate1 = strtotime($date 1);
$UTSdate2 = strtotime($date 2);

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();
$UTSdate1 = strtotime($date 1,$now);
$UTSdate2 = strtotime($date 2,$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.

Since you're specifying a specific date, instead of a relative date
string, the $now parameter won't have any effect. The output will in
any case be a standard Unix timestamp, which is the number of seconds
since Unix epoch (January 1 1970 00:00:00 GMT). In the case of the date
string "2008-02-23", the result will be the integer 1203721200, no
matter what you provide with $now.

If you had instead used, say, "+5 days", the timestamp difference would
only be measureable in microseconds, so unless you wanted extreme
precision (or you have a server that's so slow that the two instances
of strtotime() will take about 1 second to execute), I wouldn't bother
changing it.

--
Kim André Akerø
- ki******@NOSPAM betadome.com
(remove NOSPAM to contact me directly)

[=?iso-8859-1?Q?Kim_Andr=E9_Aker=F8?=]

Erwin Moller wrote:

Captain Paralytic schreef:

On 24 Apr, 09:47, Erwin Moller
<Since_humans_r ead_this_I_am_s pammed_too_m... @spamyourself.c om>

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
misunderstandin g of that relative part, and I think I keep
programming PHP.

If you look further down in the manual:

time

The string to parse, according to the GNU » Date Input Formats syntax.

The text "» Date Input Formats" links to the GNU documentation on date
input formats:
http://www.gnu.org/software/tar/manu...e/tar_113.html

In the case of pure calendar dates:
http://www.gnu.org/software/tar/manu...e/tar_115.html

And, in the case of "+5 days":
http://www.gnu.org/software/tar/manu...e/tar_119.html

--
Kim André Akerø
- ki******@NOSPAM betadome.com
(remove NOSPAM to contact me directly)