Problem adding month to a php date

Question

I’m having a certain problem adding months with php, had done using the Modify but as in the documentation itself already informs that of the error, then I tried other 3 functions I found and then the 3 bring me the same error, when a date starts in the days 29, 30 or 31 January, for example, in the month of February comes all to the day 28 (until ok there), but in the other months (March, April) should come for every created day (29, 30 or 31) and not always day 28.

How can I fix this?

Here is an example with one of these functions:

$date=new DateTime();
$date->setDate(2017,1,31);

addMonths($date, 1);
echo $date->format('d/m/Y');

echo "<br>";

addMonths($date, 1);
echo $date->format('d/m/Y');

echo "<br>";

addMonths($date, 1);
echo $date->format('d/m/Y');

function addMonths($date,$months)
{
    $init=clone $date;
    $modifier=$months.' months';
    $back_modifier =-$months.' months';

    $date->modify($modifier);
    $back_to_init= clone $date;
    $back_to_init->modify($back_modifier);

    while($init->format('m')!=$back_to_init->format('m')){
        $date->modify('-1 day')    ;
        $back_to_init= clone $date;
        $back_to_init->modify($back_modifier);
    }
}

outworking

28/02/2017
28/03/2017
28/04/2017

while the expected result would be

28/02/2017
31/03/2017
30/04/2017

Answer 1

In short, the problem is that you are changing the original instance of the start date, so this way when you add 1 month to the start date, this will be 28/02, that is, $date will become 28/02; when added another month, the day will be 28/03, as it would be adding one month on 28/02 and not two months on 31/01. To not change the object, clone the input object and modify it, returning its instance at the end:

function add_months(DateTime $date, int $months)
{
    // Clona o objeto $date para mantê-lo inalterado
    $future = clone $date;

    // Define o modificador
    $modifier = "{$months} months";

    // Modifica a data $future
    $future->modify($modifier);

    // Clona o objeto $future para corrigir o limite dos dias
    $pass = clone $future;
    $pass->modify("-{$modifier}");

    // Enquanto o mes atual for diferente do mês do passado do futuro
    while ($date->format('m') != $pass->format('m'))
    {
        // Modifica as datas em -1 dia
        $future->modify("-1 day");
        $pass->modify("-1 day");
    }

    // Retorna a data desejada
    return $future;
}

// Define a data inicial
$date = new DateTime();
$date->setDate(2017, 1, 31);

// Adiciona 1 mês à data inicial
echo add_months($date, 1)->format("d/m/Y"), PHP_EOL;

// Adiciona 2 meses à data inicial
echo add_months($date, 2)->format("d/m/Y"), PHP_EOL;

// Adiciona 3 meses à data inicial
echo add_months($date, 3)->format("d/m/Y"), PHP_EOL;

In this way, the result produced will be as expected:

28/02/2017
31/03/2017
30/04/2017

Note that instead of adding several times 1 month, you should add the correct amount of months, otherwise the problem will persist.