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Form Validation (Basic Server-Side Validation)

 

Form validation ensures that the data entered by the user is correct, complete, and safe before processing it. In server-side validation, PHP checks the submitted data after it reaches the server, making it more secure than client-side validation.

Why Server-Side Validation is Important

·         Prevents invalid or incomplete data from being stored in the database.

·         Protects against malicious input (e.g., XSS, SQL injection).

·         Works even if JavaScript is disabled in the browser.

Example: Basic Form with Validation

<?php
$name = $email = "";
$nameErr = $emailErr = "";
 
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate name
    if (empty($_POST["name"])) {
        $nameErr = "Name is required";
    } else {
        $name = htmlspecialchars($_POST["name"]);
    }
 
    // Validate email
    if (empty($_POST["email"])) {
        $emailErr = "Email is required";
    } elseif (!filter_var($_POST["email"], FILTER_VALIDATE_EMAIL)) {
        $emailErr = "Invalid email format";
    } else {
        $email = htmlspecialchars($_POST["email"]);
    }
}
?>

HTML Form:

<form method="post" action="">
    Name: <input type="text" name="name" value="<?php echo $name; ?>">
    <span style="color:red;"><?php echo $nameErr; ?></span>
    <br><br>
 
    Email: <input type="text" name="email" value="<?php echo $email; ?>">
    <span style="color:red;"><?php echo $emailErr; ?></span>
    <br><br>
 
    <input type="submit" value="Submit">
</form>

How It Works

1.      The form sends data to the same PHP page when submitted.

2.      PHP checks if each field is empty or invalid.

3.      If errors are found, they are displayed next to the respective input fields.

4.      Data is sanitized using htmlspecialchars() to prevent malicious scripts.

5.      The form retains previously entered values to improve the user experience.

Key Validation Functions in PHP

·         empty() → Checks if a field is empty.

·         filter_var($var, FILTER_VALIDATE_EMAIL) → Validates email format.

·         htmlspecialchars() → Escapes HTML special characters to prevent XSS.

·         strlen() → Checks length of strings.

 

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