PHP accessing object stored in an array

Question

I am new to taking an object oriented approach with php...actually I have a lot of learning to do overall, but the only way to learn is by doing.

So I have an array that holds several DateTime objects..I know this to be true because I have ran var_dump on the array and it indeed is holding several objects.

I need to go through each date and make sure there is never a difference greater than one day.

My research would seem to indicate that we cannot access or modify an object using the subscript operator:

$foo = $neat_array[$i+1]->format('U') ; //looking to format DateTime object as unix //this returns an error every time

Okay I am fine with that, but I simply cannot figure out the syntax to access a specific item in the array so that it is seen as an object and does not pull an error.

I have pieced together that using -> is how I need to do it, but I never get any useable result.

Here is pseudo code of what I am trying to do

foreach($date_array as $date) { //check to see if the difference between the next date in the array and the current date of the array is greater than one day. //I cannot use diff because I am on php 5.2 so I am trying this $date->format('U') and then doing the math }

@absentx - Your first example should not produce an error in PHP 5.2 (I just tested it). — nickb
– nickb, Commented Nov 15, 2011 at 0:44
Call to a member function format() on a non-object in /class_library.php on line 121 — absentx
– absentx, Commented Nov 15, 2011 at 0:58

nickb · Accepted Answer · 2011-11-16 01:03:26Z

Since learning by experimenting (and failing) is IMO a great way to learn, here is something to get you started.

$date_array = array( new DateTime("tomorrow"), new DateTime("now"), new DateTime("yesterday"), new DateTime("last day of october") ); for( $i = 0, $count = count( $date_array); $i < $count; $i += 2) { // Get the current object AND the next one in the array echo $date_array[ $i ]->format('U'); echo '<br />'; echo $date_array[ $i + 1 ]->format('U'); echo '<br />'; // Now that you have the UNIX timestamps, you can do the math you need in here. }

Note that the above will fail if the array contains an odd number of elements - I'll leave that fix up to you (if you need it).

Demo

Edit: You're probably getting that error for one of two reasons:

You're referencing an element that either isn't a DateTime object
You're referencing an element that doesn't exist in the date array

Here is a demo that shows error #2.

Edit: Here is a working example based off your answer that works for even and odd array sizes. It is essentially the same, except I don't bother with saving the values to variables or subtracting and comparing to 1 (since it's unnecessary).

$session_dates = $date_array = array( new DateTime("tomorrow"), new DateTime("yesterday"), new DateTime("now"), ); for( $i = 0, $count = count( $date_array) - 1; $i < $count; $i++) { if( ($date_array[ $i + 1 ]->format('U') - $date_array[ $i ]->format('U')) > 86400) { die( 'The date array does not contain consecutive dates.'); } }

See it in action.

See my code is very similar but it still pulls the fatal error for calling function format on a non object. Hmm, I should have posted my actual code first...how can I do that now...first time on stack
I've updated my answer with a potential explanation - You're probably accessing an element in the array that doesn't exist (by exceeding the array's bounds), which is why you're getting that error.
ahhhh...I bet is absolutely #2!! excellent point, I wanted to get past the error before I coded the loop better and I bet that is the problem, will report back...
@absentx I've updated my answer that simplifies / consolidates your code (although it is quite similar), and I've included a demo for you to test it.
@absentx You're welcome! If my post answered your question, could you mark it as accepted? Thanks.

absentx · Accepted Answer · 2011-11-15 08:28:25Z

Okay..first of all, I appreciate everyone's help. Nickb, thanks for the help and the demos. As I surmised earlier, your suggestion that I might be trying to access an element that doesn't exist in the array was absolutely the case. What I am trying to do here is a pretty important part of a site I am creating..this whole mess will serve as a function in a class that checks reservation dates.

This is my first shot at Stack Overflow, so forgive me but I probably should have put more information in my initial question, but I was convinced I knew why the code wasn't working..which was completely incorrect!

See, since I always needed to know the current element, plus the next element in the array, my code was always breaking on the very last run of the loop, because it was trying to access the current key, plus the next one (which didn't exist on the last try).

Now, the real frustrating part is I screwed around with the for loop for this code all night and I still could not get it to cleanly go through every item without breaking...I would always over-run on that last item of the array and pull the error. I think the problem all along was that I never needed to go through every item in the array, just up to the second to last item (plus check the next one) then quit the loop.

Here is my code that finally works, but I don't really like it...I have a feeling there are some simple fixes in syntax and other areas that will make this more efficient...if not, the so be it...this is by the way, basically my testing code full of echos to see what was actually happening, but it is finally doing everything right:

$count = (count($session_dates)-1); //never could get that last item to not trigger error, so subtracting one from the count was the only thing to end my frustration!!!but as I write this answer I think I see why and that is because we don't need to go through each item of the array, just each but the last item echo '<p>'.$count.' this is the count of session dates </p>'; for ($i=0; $i<$count; $i++){ $unix_one = $session_dates[$i+1]->format('U'); //make some variables that are in the date format I want to visualize for echoing $unix_echo_one = $session_dates[$i+1]->format("n".'/'."j".'/'."Y"); $unix_two = $session_dates[$i]->format('U'); $unix_echo_two = $session_dates[$i]->format("n".'/'."j".'/'."Y"); //see if the difference is greater than one day if(($unix_one-$unix_two)/86400>1){ echo 'these dates are absolutely not consecutive, you fail!!'; //we only need one occurrence to wreck what we are trying to do, so just exit if it happens. exit(); } //I needed to see if any of the loop was happening to help try and figure this out!! echo '<p>'.$unix_echo_one.'||'.$i.'||'.$unix_echo_two.'</p>'; }

perhaps this should be moved to an addendum to your initial question?
I am certainly willing to do that if indeed that is the best option...do I just edit the original question?
yes, click the little edit button and append these. I'd do it for you but I'm still a ways from edit privileges.

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