Form Validation with PHP

This article demonstrates building and validating a simple web form using HTML and PHP. The form, created with HTML, collects user data (name, address, email, fruit consumption preferences, and brochure request). PHP handles validation and processing. The goal is to illustrate basic HTML form elements and how PHP accesses their data.

The form includes text fields, radio buttons, a multiple-select list, a checkbox, and a submit button. Validation ensures all required fields are filled. Empty fields display "Missing" upon resubmission. Successful submission displays the entered data. The complete code is available on GitHub.

Key Concepts:

• PHP Form Validation: Verifies complete form submission, displaying error messages for missing data.
• $_POST Superglobal: Securely retrieves user input from forms using the POST method.
• htmlspecialchars(): Prevents Cross-Site Scripting (XSS) attacks by converting special HTML characters to their entities.
• Persistent User Selections: PHP remembers user choices in radio buttons and select lists for improved user experience.
• Advanced Validation: Suggests using libraries like laminas-validator for more robust validation.

Form Structure:

The HTML form simulates a fruit survey for "The World of Fruit," gathering user details, fruit consumption habits, and brochure preferences.

HTML Elements:

• Text Fields (name, address, email): Standard text input fields using <input type="text">.
• Radio Buttons (howMany): A group of radio buttons (<input type="radio">) for selecting fruit consumption amount (0, 1, 2, or more than 2).
• Select List (favoriteFruit): A multiple-select list (<select multiple></select>) allowing users to choose multiple favorite fruits.
• Checkbox (brochure): A checkbox (<input type="checkbox">) for brochure requests.
• Submit Button: A submit button (<input type="submit">) to send the form data.
• Form Element (<form></form>): Uses the POST method (method="POST") and action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" to send data to the same script for processing.

PHP Processing:

The PHP code validates the form data. It checks for empty required fields and stores errors in the $errors array. If no errors, it displays the submitted data. If errors exist, the form is redisplayed with error messages and pre-filled values. The code utilizes $_POST to access submitted data and htmlspecialchars() to sanitize input, preventing XSS vulnerabilities. The example provides basic validation; more robust validation (length checks, email format, date validation) is recommended using libraries like laminas-validator for production applications.

CSS Styling:

Simple CSS is used to style error messages:

<code class="language-css">.error {
  color: #FF0000;
}</code>

Improving User Experience:

The PHP code is enhanced to remember user selections in radio buttons and the select list, improving the user experience upon resubmission.

Summary:

This tutorial provides a foundation for building and validating web forms using HTML and PHP. It emphasizes secure coding practices and highlights the importance of robust validation for data integrity and security. Remember to expand upon the basic validation techniques shown here for real-world applications.

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