Why Does 'isset($_POST)' Always Return True, Even for Empty Forms?

Understanding the "If isset $_POST" Behavior

When creating forms that submit data to another page, it's essential to validate user input to ensure the form data is present and not empty. However, many developers encounter issues when checking if a form field is set using "isset()." This article explores why "isset()" may always return true, even for empty forms, and provides a solution to address this challenge.

One of the fundamental principles of web forms is that all input fields are automatically set when the form is submitted, regardless of whether they contain any value. This means that when checking if a field is filled or not, relying solely on "isset()" can be misleading.

To accurately determine if a field is empty, developers must also check for its emptiness. The "!empty()" operator can be used to accomplish this.

Here's an improved version of the code example provided in the question:

step2_check.php:

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

By using "!empty()" in this manner, the code now accurately differentiates between set but empty fields and fields that are truly not present. This ensures that the validation logic operates correctly and provides the intended behavior.

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