How can PHP developers effectively return error messages or feedback to a form after form submission and validation?

When a form is submitted and validated in PHP, developers can effectively return error messages or feedback by storing the messages in an array and then displaying them on the form page. This can be achieved by checking the validation conditions and populating the error array accordingly. The error messages can then be displayed next to the form fields that failed validation. 

<?php
$errors = [];

// Validate form submission
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Check validation conditions
    if (empty($_POST["username"])) {
        $errors["username"] = "Username is required";
    }

    if (empty($_POST["password"])) {
        $errors["password"] = "Password is required";
    }

    // If no errors, process form data
    if (empty($errors)) {
        // Process form data
    }
}

// Display form with error messages
?>
<form method="post" action="">
    <input type="text" name="username" value="<?php echo $_POST["username"] ?? ''; ?>">
    <?php if(isset($errors["username"])) { echo $errors["username"]; } ?>
    
    <input type="password" name="password" value="<?php echo $_POST["password"] ?? ''; ?>">
    <?php if(isset($errors["password"])) { echo $errors["password"]; } ?>
    
    <input type="submit" value="Submit">
</form>

Keywords

PHP form submission validation error messages feedback

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