loop through dates

[NZ_Kiwis]

this only echo's the 1st of Jan not the other 30 days, why?

$startDate = date('2012-01-01');
$endDate = date('2012-01-31');

$currentDate = $startDate;

do {
	echo $currentDate;

$currentDate = strtotime(date("Y-m-d", strtotime($currentDate)) . " +1 day");
} while ($currentDate < $endDate);

[bradgrafelman]

Well for one, this doesn't make much sense:

$startDate = date('2012-01-01'); 
$endDate = date('2012-01-31');

You might as well have written:

$startDate ='2012-01-01'; 
$endDate = '2012-01-31';

since you aren't actually using date() in any way.

Next, note that PHP isn't as intelligent as MySQL is when it comes to inequalities involving dates, mostly because PHP isn't aware of the difference between a date string (like '2012-01-01') and the string "Watermelons are really tasty!"... mostly because there really is no difference at some level; they're both just strings, after all.

As such, this comparison:

$currentDate < $endDate

would appear to be comparing two strings initially (and, after the first iteration, one number and one string) numerically, which doesn't make much sense. (Is "Watermelons are really tasty!" greater than, less than, or equal to "Hello world." ?)

In the end, I would suggest going about this a different way; take a look at PHP's [man]DateTime[/man], [man]DateInterval[/man], and [man]DatePeriod[/man] classes. The basic process would be something like:

1. Create two instances of the [man]DateTime[/man] class - one each for the starting and ending dates.

2. Create an instance of the [man]DateInterval[/man] class to describe the desired interval between dates (e.g. 1 day).

3. Create an instance of the [man]DatePeriod[/man] class, supplying the above objects as described in the class' constructor (see: [man]DatePeriod.construct[/man]).

4. "Traverse" (fancy word for what we commonly use the phrase "loop through", i.e. "loop through the array with a foreach() loop") the object, e.g. using a [man]foreach[/man] loop, and output each [man]DateTime[/man] object returned in each iteration.

   The first (and, presently, only) user comment on the [man]DatePeriod.construct[/man] man page pretty much illustrates this usage of the DatePeriod class, so you could heavily rely on that as an example of what you're trying to do.

[NZ_Kiwis]

I've found another way of doing this, i'll share once completed.
What I have though is a timestamp for each day, it's 0812 on each day though as it's the time it was run.

How can I now convert this into the time as of 0001 that morning and another one for 2359 that night?

[NZ_Kiwis]

I have this

$startDate = mktime(0, 0, 0 , 1, 1, 2012);
$endDate = mktime(0, 0, 0 , 2, 3, 2012);
$c = 0;


for ($startDate; $startDate <= $endDate; $startDate += 86400) {
 	$s = mktime(0, 0, 1, date('m', $startDate), date('j', $startDate), date('Y', $startDate));
	$e = mktime(23, 59, 59, date('m', $startDate), date('j', $startDate), date('Y', $startDate));

[Weedpacket]

for ($startDate; $startDate <= $endDate; $startDate += 86400) {

You do realise that not all days are 86,400 seconds long, don't you? You'll end up skipping some days and duplicating others.

[NZ_Kiwis]

Weedpacket;10995914 wrote:

for ($startDate; $startDate <= $endDate; $startDate += 86400) {

You do realise that not all days are 86,400 seconds long, don't you? You'll end up skipping some days and duplicating others.

But it it was only every looking at 4-5 weeks would 86,400 really get a wrong date?

For example; if I looked at midday on the first day and went forward 86,400 seconds - I'll always hit the next day but never far enough to miss a day or never not far enough so it hits the same day.

Can you see a issue with that?

[Weedpacket]

But you're not looking at midday, you're looking at midnight. If the day is 90,000 seconds long then going forward only 86,400 won't be enough to get you to the next day.

Did you read bradgrafelman's post? Why are you trying to reproduce all this stuff by hand when PHP already provides classes that implement it?

$start = new DateTime('2012-01-01');
$end = new DateTime('2012-01-31');
$end->modify('+1 day'); // Date Periods are right-open intervals

$period = new DatePeriod($start, new DateInterval('P1D'), $end);
foreach($period as $day)
{
	echo $day->format('Y-m-d'), "\n";
}

[NZ_Kiwis]

Weedpacket;10995918 wrote:

But you're not looking at midday, you're looking at midnight. If the day is 90,000 seconds long then going forward only 86,400 won't be enough to get you to the next day.

Did you read bradgrafelman's post? Why are you trying to reproduce all this stuff by hand when PHP already provides classes that implement it?

$start = new DateTime('2012-01-01');
$end = new DateTime('2012-01-31');
$end->modify('+1 day'); // Date Periods are right-open intervals

$period = new DatePeriod($start, new DateInterval('P1D'), $end);
foreach($period as $day)
{
	echo $day->format('Y-m-d'), "\n";
}

Because I didn't understand the DatePeriod and DateInterval classes

[Weedpacket]

NZ_Kiws wrote:

Because I didn't understand the DatePeriod and DateInterval classes

Funnily enough I was the same once; I must lack the "innate understanding of the DatePeriod and DateInterval classes" gene as well. I had to read the documentation about them and try a few things out first. It might have taken me all of half an hour's worth of study, though I didn't exactly have a stopwatch running.

[Derokorian]

Indeed I used to avoid the DateTime class and its relatives (why I'm not sure) but once I spent a little bit of time and read the docs and tried it out, I found much more intuitive and easier to work with.

[NZ_Kiwis]

What I don't get it how from:

http://nz.php.net/DateInterval
http://nz.php.net/DatePeriod

you get this,

$period = new DatePeriod($start, new DateInterval('P1D'), $end); 

How did you know P1D?
How did you know DatePeriod had a DateInterval inside it?

[Derokorian]

With DateInterval, when looking at the page and having a fair grasp of OOP I thought I should look at the construct. Which is linked to from the page you linked DateInterval::construct I then read the parameter list:

public DateInterval::__construct() ( string $interval_spec )

Scrolled down just a little bit further to see that this interval_spec was specified and defined as:

interval_spec
Interval specification.

The format starts with the letter P, for "period." Each duration period is represented by an integer value followed by a period designator. If the duration contains time elements, that portion of the specification is preceded by the letter T.

interval_spec Period Designators
Period Designator Description
Y years
M months
D days
W weeks. These get converted into days, so can not be combined with D.
H hours
M minutes
S seconds
Here are some simple examples. Two days is P2D. Two seconds is PT2S. Six years and five minutes is P6YT5M.

Note:

The unit types must be entered from the largest scale unit on the left to the smallest scale unit on the right. So years before months, months before days, days before minutes, etc. Thus one year and four days must be represented as P1Y4D, not P4D1Y.

[Weedpacket]

To answer your three questions in reverse order:

NZ_Kiwis wrote:

How did you know DatePeriod had a DateInterval inside it?

I looked at http://nz.php.net/DatePeriod and read the following line in the synopsis at the top of the page:

public __construct ( DateTime $start , DateInterval $interval , DateTime $end [, int $options ] )

How did you know P1D?

Derokorian has already answered this one. Also, as it happens, in the user comment to which bradgrafelman points, there is some code, the first line of which reads:

$i = new DateInterval('P1D'); 

$i is then used in constructing a DatePeriod.

What I don't get it how from:

http://nz.php.net/DateInterval
http://nz.php.net/DatePeriod

you get this,
PHP Code:

$period = new DatePeriod($start, new DateInterval('P1D'), $end); 

Frankly, that's mainly due to a couple of skills that I've developed and have come to rely upon heavily: reading and programming.