是否允许回显NULL值是一种好的做法？

Question

So I'm trying to save input values from a form in case the page reloads and I'm setting the initial value at the start of the script like like so:

$username = "";
$password = "";
$password_confirmation = "";
$email = "";
$email_confirmation = ""; 
$business_name = "";

Then if the form has been submitted and the server request method has been set to "POST" I set every individual variable to its corresponding value like so:

$username= filter_input(INPUT_POST, "username", FILTER_SANITIZE_STRING);
etc...

Then on each input element I'm echoing the corresponding value:

<input type="text" id="username" name="username" placeholder="Username" value="<?php echo $username; ?>">

So my question is, if for some reason filter_input fails and returns a NULL value and if I echo that NULL value will I have any trouble?

Answer 1

You should set a ternary method to get the value of the page on reload.

Sample:

your code

View index page

<form action="index.php" method="post">
       <input type="text" id="username" name="username" placeholder="Username" value="<?php echo $username; ?>">
<input type="submit" value="submit">
</form>

If you want to reload the value of the textbox after you submit you dont need to place a null value, instead check if the textbox has been posted or not. You can do this,

<form action="index.php" method="post">
       <input type="text" id="username" name="username" placeholder="Username" value="<?php isset($_POST["username"]) ? echo $username : echo ""; ?>">
<input type="submit" value="submit">
</form>

it means if the username has been posted, it already exist so it is set, therefore you will re take the value, else it will just display an empty box.

Hope this help for cleaner and more efficient coding.