Why Does `isset($_POST)` Return True for Empty Form Inputs?

Understanding the "If isset $_POST" Problem

When working with HTML forms and PHP, checking if a form input has been set is done using the isset() function. However, in certain scenarios, it may return a positive result even when the form field is empty. This can lead to unexpected behavior in your code.

The Issue

In the provided example, the form input named "mail" is always set, regardless of whether it contains data. This is because most form inputs are automatically set when the form is submitted, even if they are left blank.

The Solution

To address this issue, you need to check for both the existence of the input and its emptiness. This can be achieved using the !empty() function.

The corrected code:

<?php
if (!empty($_POST["mail"])) {
    echo "Yes, mail is set";    
} else {  
    echo "No, mail is not set";
}
?>

In this code, the !empty() function checks if the $_POST["mail"] variable is empty. If it is not empty, it means that the input field contains data and is set. Otherwise, it will return false and indicate that the input is not set.

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