PHP Interview Questions and Answers for 5 years experience

1. What are the different ways to include a PHP file into another PHP file?

   • Answer: There are three main ways: `include()`, `require()`, and `include_once()`/`require_once()`. `include()` and `require()` both include the specified file. The difference is that `require()` will halt execution with a fatal error if the file cannot be found, while `include()` will only issue a warning and continue. `include_once()` and `require_once()` are similar, but they only include the file once, preventing duplicate inclusions if the same file is included multiple times.

2. Explain the difference between `==` and `===` in PHP.

   • Answer: `==` performs loose comparison, checking only for equality of value. `===` performs strict comparison, checking for both equality of value and equality of type. For example, `1 == "1"` is true (loose), but `1 === "1"` is false (strict) because one is an integer and the other is a string.

3. What are magic methods in PHP and give examples?

   • Answer: Magic methods are special methods in PHP classes that start with two underscores (`__`). They allow you to perform actions automatically in response to specific events. Examples include `__construct()` (constructor), `__destruct()` (destructor), `__get()` and `__set()` (for property access), `__call()` (for method calls), and `__toString()` (for converting an object to a string).

4. How do you handle exceptions in PHP?

   • Answer: PHP uses `try`, `catch`, and `finally` blocks to handle exceptions. Code that might throw an exception is placed in a `try` block. `catch` blocks handle specific exceptions. The `finally` block always executes, regardless of whether an exception was thrown or caught, providing a cleanup mechanism.

5. What are namespaces in PHP and why are they useful?

   • Answer: Namespaces help organize code by providing a way to group classes, functions, and constants under a unique name. This prevents naming conflicts when using multiple libraries or frameworks that might have classes or functions with the same name. They are declared using the `namespace` keyword.

6. Explain the difference between PDO and MySQLi.

   • Answer: Both PDO (PHP Data Objects) and MySQLi (MySQL Improved) are database extensions in PHP, but PDO is database-agnostic, meaning it can be used with various database systems (MySQL, PostgreSQL, SQLite, etc.) with minimal code changes. MySQLi is specific to MySQL and offers features like prepared statements and object-oriented access.

7. What are prepared statements and why are they important for security?

   • Answer: Prepared statements are pre-compiled SQL statements that are stored by the database server. They are used to prevent SQL injection vulnerabilities. Instead of directly embedding user inputs into the SQL query, prepared statements use placeholders, making it safe to insert user-provided data without risking injection attacks.

8. How do you work with sessions in PHP?

   • Answer: Sessions are used to store data for a specific user across multiple page requests. They are started using `session_start()`. Data is stored in the `$_SESSION` superglobal array. Session data is typically stored on the server.

9. Explain the concept of object-oriented programming (OOP) in PHP.

   • Answer: OOP is a programming paradigm that organizes code around "objects" that contain data (properties) and methods (functions) that operate on that data. Key OOP concepts in PHP include classes (blueprints for objects), objects (instances of classes), inheritance (creating new classes based on existing ones), encapsulation (hiding internal data), and polymorphism (allowing objects of different classes to be treated as objects of a common type).

10. What is an autoloader in PHP?

    • Answer: An autoloader is a function that automatically loads classes when they are needed, instead of requiring manual `include` or `require` statements for each class. This makes code more organized and easier to manage, especially in larger projects.

11. What is the difference between `foreach` and `for` loops?

    • Answer: `foreach` is specifically designed for iterating over arrays and objects, whereas `for` is a general-purpose loop that can be used for various iterative tasks. `foreach` is more concise and readable when working with arrays, while `for` offers more control over the iteration process.

12. How do you handle file uploads in PHP?

    • Answer: File uploads are handled using the `$_FILES` superglobal array. This array contains information about uploaded files, including their name, size, type, and temporary location. PHP provides functions to move uploaded files to a permanent location and perform validation checks on the files.

13. What are some common PHP frameworks?

    • Answer: Popular PHP frameworks include Laravel, Symfony, CodeIgniter, Yii, and CakePHP. These frameworks offer structures and tools to streamline the development process.

14. Explain the concept of MVC (Model-View-Controller).

    • Answer: MVC is a software design pattern that separates the application into three interconnected parts: the Model (data and business logic), the View (user interface), and the Controller (handling user input and updating the model and view).

15. How do you use Composer in PHP?

    • Answer: Composer is a dependency manager for PHP. It's used to declare project dependencies in a `composer.json` file and automatically download and manage those dependencies. This simplifies the process of including external libraries in your project.

16. What is PSR in PHP?

    • Answer: PSR stands for PHP Standards Recommendations. These are coding standards and best practices that aim to improve interoperability and consistency across different PHP projects. Following PSR guidelines helps ensure better code readability and maintainability.

17. How do you handle database transactions in PHP?

    • Answer: Database transactions are used to ensure that a set of database operations are treated as a single unit of work. If any operation fails, the entire transaction is rolled back, maintaining data consistency. This is typically done using `beginTransaction()`, `commit()`, and `rollBack()` methods in database libraries like PDO.

18. What are some common security best practices in PHP?

    • Answer: Common security practices include using prepared statements to prevent SQL injection, escaping user input to prevent cross-site scripting (XSS) attacks, validating user inputs, using strong passwords and proper password storage techniques, and keeping your PHP installation and libraries up-to-date.

19. What are anonymous functions (closures) in PHP?

    • Answer: Anonymous functions are functions without a name. They are defined using the `function` keyword followed by the function code, and can be assigned to variables or passed as arguments to other functions. They can access variables from the surrounding scope (closures).

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