PHP interview questions
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1. What is PHP and why is it used?
Answer: PHP (Hypertext Preprocessor) is a popular, open-source server-side scripting language used for developing static or dynamic web applications. It is embedded within HTML and is known for its fast performance, extensive database support, and compatibility with various operating systems.
2. How do you declare a variable in PHP?
Answer: Variables in PHP are declared with a dollar sign ($) followed by the variable name. They do not need to be declared before being used, although it's considered good practice to do so.
$variableName = "value";
3. Explain the difference between `GET` and `POST` methods in form submission.
Answer: `GET` appends form data into the URL in name/value pairs, making it visible in the browser's address bar, and is limited in the amount of information it can send. `POST` sends the form data as HTTP post transactions, which do not appear in the URL and have no limit on the amount of information sent.
4. What are sessions in PHP and how do they work?
Answer: Sessions in PHP are a way to store information (in variables) to be used across multiple pages. Session variables hold information about one single user and are available to all pages in one application. A session is started with the `session_start()` function.
5. Describe what cookies are and how they are used in PHP.
Answer: Cookies are small files that the server embeds on the user's computer. Each time the same computer requests a page with a browser, it will send the cookie too. With PHP, you can both create and retrieve cookie values.
6. Explain the use of the `include` and `require` statements.
Answer: Both `include` and `require` statements are used to insert the content of one PHP file into another. The difference is that `require` will produce a fatal error and stop the script execution if the file cannot be included, while `include` will only produce a warning and the script will continue.
7. What is the difference between `==` and `===` operators?
Answer: `==` is the equality operator that checks if the values of two operands are equal, ignoring their types. `===` is the identity operator that checks both the values and types of the operands.
8. How do you connect to a MySQL database in PHP?
Answer: You can connect to a MySQL database using the `mysqli_connect()` function or the PDO (PHP Data Objects) approach. Here's an example using mysqli_connect():
$connection = mysqli_connect("hostname", "username", "password", "databaseName");
9. Explain what PDO is and its advantages.
Answer: PDO (PHP Data Objects) is a database access layer providing a uniform method of access to multiple databases. It does not provide database-specific features, making it possible to create code that can handle different types of databases. Advantages include usability, security (prepared statements), and reusability.
10. What are Prepared Statements and how do they work?
Answer: Prepared Statements are a feature used to execute the same (or similar) SQL statements repeatedly with high efficiency. They work by preparing the SQL statement first and then binding the parameters. This improves security by avoiding SQL injection and improves performance by pre-compiling the SQL statement.
11. Describe the visibility of property or method in OOP.
Answer: Visibility of a property or a method in OOP is defined by the keywords `public, protected, or private. Public` means the member can be accessed from anywhere, `protected` means it can be accessed within the class itself and by inheriting and parent classes, and `private` means it can only be accessed by the class that defines the member.
12. What is inheritance in PHP?
Answer: Inheritance in PHP is a concept where one class (child class) can inherit properties and methods of another class (parent class). This helps in reducing code duplication and improves code organization.
class ParentClass { // Parent class methods and properties } class ChildClass extends ParentClass { // Child class can use parent class methods and properties }
13. Explain what a namespace is in PHP and why it's used.
Answer: Namespaces are a way of encapsulating items in PHP. They are used to solve two primary problems: name collisions between code you create, and PHP internal classes/functions/constants, or third-party classes/functions/constants; and the ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem,
improving readability of source code.
14. What are traits in PHP?
Answer: Traits are a mechanism for code reuse in single inheritance languages like PHP. A Trait is intended to reduce some limitations of single inheritance by enabling a developer to reuse sets of methods freely in several independent classes living in different class hierarchies.
15. How do you handle errors in PHP?
Answer: PHP handles errors primarily through the use of the `try` `catch` block. You can also handle errors by setting a custom error handler function with set_error_handler().
try { // Code that may throw an exception } catch (Exception $e) { // Code to handle the exception }
16. What is the use of the `final` keyword?
Answer: The `final` keyword can be used to prevent class inheritance and to prevent method overriding.
17. Explain what late static bindings are in PHP.
Answer: Late static bindings in PHP are used to reference the called class in a context of static inheritance. It's a way to ensure static methods and properties are referenced in the context of the calling class, not the class where they are defined.
18. What is the difference between `echo` and print?
Answer: Both `echo` and `print` are used to output data to the screen. The differences are minimal: `echo` has no return value, can take multiple parameters, and is marginally faster than print, which has a return value of 1 and can only take one argument.
19. Describe the `foreach` loop.
Answer: The `foreach` loop is used for iterating over elements of an array or an object. For each iteration, the value of the current element is assigned to `$value` and the internal array pointer is advanced by one (so the next element will be processed in the next iteration).
foreach ($array as $value) { // Code to be executed }
20. How can you prevent SQL injection in PHP?
Answer: SQL injection can be prevented by using prepared statements and parameterized queries. These SQL statements are sent to and parsed by the database server separately from any parameters, which makes it impossible for an attacker to inject malicious SQL.
21. What are magic methods in PHP?
Answer: Magic methods are special methods that have specific names starting with double underscore __. Examples include __construct(), __destruct(), __call(), __get(), __set(), and more. They are triggered in response to specific actions like creating or cloning an object, accessing a property, etc.
22. Explain what MVC architecture is.
Answer: MVC (Model-View-Controller) architecture is a design pattern used in software engineering to separate the application logic into three interconnected components. This separation helps manage complexity, promotes organized coding, and allows multiple developers to work simultaneously on different components without affecting each other.
23. What is the `__construct()` method in PHP?
Answer: The `__construct()` method is a magic method that is automatically called when a new instance of a class is created. It typically contains initializations required for the object.
24. How do you create a constant in PHP?
Answer: Constants in PHP are created using the `define()` function or the `const` keyword inside a class. Once a constant is defined, it cannot be changed or undefined.
define("CONSTANT_NAME", "value"); // or inside a class const CONSTANT_NAME = 'value';
25. Explain the use of `header()` function in PHP.
Answer: The `header()` function is used to send a raw HTTP header to a client. It's commonly used for page redirection or to set content-type headers.
26. What is Composer in PHP?
Answer: Composer is a dependency manager for PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you.
27. Describe how to send an email using PHP.
Answer: PHP uses the `mail()` function to send an email. This function requires four arguments to send an email: the recipient's email address, the subject of the email, the message, and additional headers.
mail('recipient@example.com', 'Subject', 'Message', 'From: sender@example.com');
28. What are PHP filters used for?
Answer: PHP filters are used to validate and sanitize external input. The filter functions used for data validation and sanitization ensure that an application gets the correct input type and format.
29. Explain the difference between static and dynamic websites.
Answer: Static websites consist of fixed content where each page displays the same information to all visitors. Dynamic websites contain web pages that are generated in real-time. These pages include Web scripting
code, such as PHP or JavaScript, which dictates the content to display or the actions to take.
30. How do you start and end a PHP block of code?
Answer: A PHP block of code starts with ``. If the PHP file only contains PHP code, it is recommended to omit the closing tag to prevent accidental whitespace or new lines being sent to the browser.
<?php // PHP code goes here
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