Sharpen Your Skills: Essential PHP Interview Questions and Answers

PHP (Hypertext Preprocessor) remains one of the most widely used server-side scripting languages, powering millions of websites and web applications. Whether you're a seasoned PHP developer or just starting your career, preparing for a PHP interview can be a difficult task. To help you get ready, here’s a list of the most common PHP interview questions, covering basic to advanced topics.

Basic PHP Interview Questions

1. What is PHP?

PHP stands for Hypertext Preprocessor. It is an open source server-side scripting language which is widely used to develop dynamic web pages and web applications. It supports many databases like MySQL, Oracle, Sybase, Solid, PostgreSQL, generic ODBC etc.

2. What was the old name of PHP?

Personal Home Page.

3. What are the main features of PHP?

• Open Source
• Cross-Platform Compatibility
• Simple and Easy to Learn
• Supports Various Databases
• Strong Community Support
• Embedding Capability with HTML

4. What are the differences between PHP4 and PHP5?

PHP5 introduced new features such as improved support for object-oriented programming (OOP), PDO (PHP Data Objects) for database access, improved error handling with exceptions, and better support for XML and MySQL.

5. What is the difference between echo and print in PHP?

echo can output multiple strings and does not return a value, while print can only output one string and always returns 1.

6. How do you declare a PHP variable?

PHP variables are declared with a $ sign followed by the variable name. For example: $variableName.

7. What are superglobals in PHP?

Superglobals are built-in variables that are always accessible, regardless of scope. They include $_GET, $_POST, $_REQUEST, $_SESSION, $_COOKIE, $_SERVER, $_FILES, and $_ENV.

8. How to include a file to a PHP page?

We can include a file using "include() " or "require()" function with file path as its parameter.

Intermediate PHP Interview Questions

9. What is the difference between == and === in PHP?

== is the equality operator and checks if the values of two operands are equal, ignoring their type. === is the identity operator and checks if the values and types of two operands are identical.

10. What is a PHP session and how do you start one?

A PHP session is a way to store data across multiple pages. You start a session with the session_start() function at the beginning of your script.

11. How do you connect to a MySQL database using PHP?

Using the mysqli_connect() function or PDO (PHP Data Objects). For example:

$conn = mysqli_connect("localhost", "username", "password", "database");
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

12. What are PHP namespaces and why are they important?

Namespaces allow you to encapsulate items such as classes, functions, and constants to avoid name collisions. They are defined using the namespace keyword.

13. What is the use of the final keyword in PHP?

The final keyword can be used to mark a class or method so that it cannot be extended or overridden.

14. Explain the concept of traits in PHP

Traits are a mechanism for code reuse in single inheritance languages like PHP. They allow you to include methods in a class without using inheritance.

15. What's the difference between include and require?

Both require and include are used to include files, but require will produce a fatal error and stop the script if the file cannot be included, whereas include will only produce a warning and the script will continue.

16. How to set cookies in PHP?

Setcookie("sample", "ram", time()+3600)

17. How to Retrieve a Cookie Value?

echo $_COOKIE["user"]

18. How will you delete a cookie?

To delete a cookie you should call set cookie() with the name argument only.

19. Is multiple inheritance supported in PHP?

PHP supports only single inheritance; it means that a class can be extended from only one single class using the keyword extended.

20. What are rules for naming a PHP variable?

Rules for naming a variable are following − Variable names must begin with a letter or underscore character. A variable name can consist of numbers, letters, underscores but you cannot use characters like + , - , % , ( , ) . & , etc.

21. Which function will you use to create an array?

array() − Creates an array.

22. How can you sort an array?

sort() − Sorts an array.

Advanced PHP Interview Questions

23. What is the purpose of the composer in PHP?

Composer is a dependency management tool for PHP. It allows you to manage the libraries your project depends on and can handle autoloading of classes.

24. How do you handle exceptions in PHP?

Using try-catch blocks. For example:

try {
    // Code that may throw an exception
} catch (Exception $e) {
    // Handle the exception
    echo 'Caught exception: ',  $e->getMessage(), "\n";
}

25. What is the use of PDO in PHP?

PDO (PHP Data Objects) is a database access layer providing a uniform method of access to multiple databases. It supports prepared statements, which help prevent SQL injection attacks.

26. What are the differences between abstract classes and interfaces in PHP?

An abstract class can have both abstract methods (without implementation) and concrete methods (with implementation), whereas an interface can only have abstract methods. A class can inherit multiple interfaces but only one abstract class.

27. Explain the Singleton design pattern in PHP

The Singleton pattern restricts the instantiation of a class to one object. It involves a private constructor, a static method to get the instance, and a static variable to hold the instance.

28. What is the purpose of the __autoload function in PHP?

The __autoload function is a magic function that is automatically called when trying to instantiate a class that hasn't been defined yet. However, it is deprecated as of PHP 7.2.0 in favor of spl_autoload_register().

29. What are closures in PHP?

Closures are anonymous functions that can capture variables from the surrounding scope. They are created using the function keyword without a function name.

30. How does PHP handle error reporting?

PHP handles error reporting using the error_reporting() function and the ini_set() function to configure error levels. Errors can be logged to a file or displayed on the screen.

Remember, this list provides a starting point. Be prepared for variations and in-depth discussions on these topics. Additionally, here are some tips for acing your interview:

• Practice your coding skills: Brush up on your ability to write clean and efficient PHP code.
• Research the company and role: Tailor your answers to demonstrate your understanding of their specific needs.
• Articulate your thought process: Explain your thought process and problem-solving approach during coding challenges.
• Ask insightful questions: Demonstrate your curiosity and genuine interest in the role and the company.

Conclusion

Preparing for a PHP interview involves understanding both fundamental and advanced concepts. This list of common PHP interview questions covers a wide range of topics, from basic syntax and functions to advanced OOP concepts and design patterns. Reviewing and practicing these questions can help you feel more confident and ready to tackle your next PHP interview.