Date function with two variables

Question

I’m trying to concatenate a date and time to get the value (ISO) in Mysql so I can insert them into the database. The code line is this:

Example: datai = 20/04/2018 and horai = 14:27

$data = '$_POST[datai]';
$data2 = date("Y-m-d", strtotime($data)); // converter para formato definido
$hora = '$_POST[horai]'.':00'; // adicionar segundos à hora
$datahora = date('Y-m-d H:i:s', strtotime($data2.''.$hora));

However, what is received in the comic is:

1970-01-01 01:00:00

Can you explain to me if it is possible to concatenate date and time in this way? They are two different inputs.

The query to the database is this:

$inserirdatahora = mysqli_query ($conexao,"UPDATE minha_tabela 
SET data_de_inicio = '$datahora' WHERE (id = 10)");

Answer 1

Yes, it is possible, but as you defined $data as '$_POST[datai]', the variable will receive the string '$_POST[datai]' literal, not the value of $_POST['datai'], because you used simple quotes. As the function strtotime does not recognize this pattern, instead of giving error it will set the default date (typical PHP does not warn the developer that something is wrong). The same goes for $_POST['horai'].

PHP only evaluates the value of a variable within string when double quotation marks are used, as in "Você informou a data {$data}", However, in this case, why the quotes? All data that comes with the HTTP request, by definition, are string, then it is unnecessary to do "$_POST['datai']".

The correct alternative would be:

$data = $_POST['datai'];
$hora = $_POST['horai']; // amém
$datahora = date('Y-m-d H:i:s', strtotime("{$data} {$hora}"));

Answer 2

Response that transforms two variables into one and converts from dd/mm/yyyy for yyyy-mm-dd and adds two '0' at the end of the time (from 8:00 to 08:00:00).

$date1 = strtr($_POST['datai'], '/', '-');
$date2 = date('Y-m-d', strtotime($date1));
$hora = $_POST['horai'].':00';
$datahora = date('Y-m-d H:i:s', strtotime("{$date2} {$hora}"));