Manuel João Silva

So I just spent almost a day chasing a (what I thought it was) a bug in my code regarding dates.

I needed to add a month to a specific date  so I can bill ongoing contracts, but the returned date sometimes where full “calendar” months other times it was 31 days.

Let me show:

echo date("Y-m-d", strtotime("+1 month 2011-11-21"));
returns: 2011-12-21 // appears to be right

echo date("Y-m-d", strtotime("+1 month 2011-11-30"));
returns: 2011-12-30 // wtf? but I wanted 2011-12-31

echo date("Y-m-d", strtotime("+1 month 2011-12-15"));
returns:  2012-01-15 // hum? that is right

echo date("Y-m-d", strtotime("+1 month 2012-01-31"));
returns: 2012-03-02 // wtf? I wanted 2012-02-29

echo date("Y-m-d", strtotime("+1 month 2012-01-01"));
returns: 2012-02-01 // oh! that's right

echo date("Y-m-d", strtotime("+1 month 2012-02-01"));
returns: 2012-03-01 // sigh... That's right to what's going on here?

As you can see above sometimes PHP return full calendar months other 31 days. Fortunately there’s a pattern:

The way I see it if the day is not in the end of the month PHP will add a calendar month if it’s in the end of the month PHP will add the number of days that the current month has.

So if you want to make sure PHP always adds a calendar month to your date this is how I did it:

$tmp_date1 = strtotime("+1 day", strtotime("2012-01-31"));
$tmp_date2 = strtotime("+1 month", $tmp_date1);
$final_date = date('Y-m-d', strtotime("-1 day", $tmp_date2));

This ensures that if your date is in the end of the month strtotime will make calculation with the beginning of the month that way full calendar months will be added instead of number of days that current month has.

Reddit discussion about this

Question: Could this be written better?

private function compareThree($val_1, $val_2, $val_3)
{
    return (($val_1 == $val_2) && ($val_1 == $val_3) && ($val_2 == $val_1) && ($val_2 == $val_3) && ($val_3 == $val_2) && ($val_3 == $val_1));
}

Short Answer: Yes! That’s horrible and makes my eyes bleed.

Long Answer: Why compare only three? Why not build a function that compares a infitine number of arguments and check if they are all equal. Here’s my solution:

function compareAllTheArguments()
{
    return count(array_unique(func_get_args())) === 1;
}

Explanation:

func_get_args() // Get all function arguments in array list

 array_unique() // Removes duplicate values from an array

count() // Well, yeah, returns the number of elements in a array

Knowing this first we get all the arguments in the function then remove all the duplicates and if it’s only one left that means all elements are equal.

The fastest and the correct way to get the last key from an array is:

$lastkey = array_pop(array_keys($arr));

Example:

$arr[] = array("red" => "apple", "yellow" => "banana");

Let’s say you want to add another element to the previous created array, for that you need to know the last created index so:

$lastkey = array_pop(array_keys($arr));
$arr[$lastkey]["brown"] = "kiwi";

And there you have it.