Top 100 PHP Developer Interview Questions and Answers for 2025

Top 100 PHP Developer Interview Questions and Answers for 2025

Prepare for your PHP developer interview with these 100 essential questions and answers. Covers basics, advanced topics, OOP, database handling, security, and more!

Basic PHP Questions

1. What is PHP?
   Answer: PHP stands for Hypertext Preprocessor. It is a server-side scripting language used to develop dynamic and interactive web applications.
2. What are the main features of PHP?
   Answer: Open-source, platform-independent, easy integration with databases, and support for various protocols (HTTP, FTP, etc.).
3. What is the difference between echo and print?
   Answer: Both are used to output data. echo is faster and does not return a value, while print returns a value (1) and is slightly slower.
4. What are PHP variables?
   Answer: Variables in PHP are containers for storing data. They start with a $ sign and are loosely typed.
5. How is PHP executed?
   Answer: PHP code is executed on the server, and the result is sent to the browser as plain HTML.

PHP Syntax and Data Types

6. What are the data types supported in PHP?
   Answer: String, Integer, Float, Boolean, Array, Object, NULL, and Resource.
7. Explain the difference between single-quoted and double-quoted strings in PHP.
   Answer: Single-quoted strings do not parse variables or escape sequences, while double-quoted strings do.
8. What are constants in PHP?
   Answer: Constants are variables that once defined cannot be changed. They are defined using define() or const.
9. How do you declare an array in PHP?
   Answer: $arr = array("value1", "value2"); or $arr = ["value1", "value2"];.
10. What is a NULL value in PHP?
    Answer: NULL is a special data type that represents a variable with no value.

Control Structures and Functions

11. What is the difference between include and require?
    Answer: Both include files in a script. If the file is missing, require throws a fatal error, while include throws a warning.
12. What is the difference between include_once and require_once?
    Answer: These ensure the file is included only once during execution, avoiding redundancy. The behavior difference is the same as include vs. require.
13. What are PHP functions?
    Answer: Functions are blocks of reusable code that perform a specific task. Example:

    function greet($name) {
        return "Hello, $name!";
    }
    

14. What is the difference between isset() and empty()?
    Answer: isset() checks if a variable is set and not NULL. empty() checks if a variable is empty (0, “”, NULL, etc.).
15. What is the purpose of die() in PHP?
    Answer: The die() function stops script execution and outputs a message.

OOP in PHP

16. What is Object-Oriented Programming (OOP)?
    Answer: OOP is a programming paradigm using objects and classes to organize code into reusable components.
17. What is a class in PHP?
    Answer: A class is a blueprint for objects. Example:

    class Car {
        public $color;
        public function drive() {
            echo "Driving";
        }
    }
    

18. What are access modifiers in PHP?
    Answer: public, protected, and private define the visibility of properties and methods.
19. What is inheritance in PHP?
    Answer: Inheritance allows a class to use properties and methods of another class using the extends keyword.
20. What is the use of the __construct() method?
    Answer: It is a magic method used to initialize class properties during object creation.

Advanced PHP

21. What are PHP sessions?
    Answer: Sessions store user information across multiple pages. Example:

    session_start();
    $_SESSION['user'] = 'John';
    

22. What is the difference between GET and POST?
    Answer: GET appends data to the URL and is less secure, while POST sends data in the request body and is more secure.
23. What is the PDO extension?
    Answer: PDO (PHP Data Objects) is a database access layer that provides a uniform method for database operations.
24. How do you handle errors in PHP?
    Answer: Use try-catch blocks or custom error handlers.
25. What is a namespace in PHP?
    Answer: Namespaces prevent name conflicts by grouping classes, functions, and constants. Example:

    namespace App\Controllers;
    

Database and SQL

26. How do you connect to a database in PHP?
    Answer: Using mysqli or PDO. Example:

    $conn = new mysqli("localhost", "user", "password", "db");
    

27. What is SQL injection? How do you prevent it?
    Answer: SQL injection is an attack where malicious SQL is executed. Prevent it by using prepared statements or parameterized queries.
28. What is the difference between mysqli_connect and PDO?
    Answer: mysqli is specific to MySQL, while PDO supports multiple databases.
29. How do you fetch data from a database in PHP?
    Answer: Using mysqli_query() or PDO’s prepare() and execute() methods.
30. What is the difference between fetch_assoc() and fetch_object()?
    Answer: fetch_assoc() returns an associative array, while fetch_object() returns an object.

File Handling

31. How do you read a file in PHP?
    Answer: Using functions like fopen(), fread(), or file_get_contents().
32. How do you write to a file in PHP?
    Answer: Using fopen(), fwrite(), and fclose() functions.
33. What is the use of file_exists()?
    Answer: Checks if a file exists before performing operations on it.
34. What is chmod() in PHP?
    Answer: It changes file permissions.
35. How do you delete a file in PHP?
    Answer: Using the unlink() function.

Security

36. How do you prevent XSS in PHP?
    Answer: Use htmlspecialchars() or strip_tags() to sanitize input.
37. How do you hash passwords in PHP?
    Answer: Use password_hash() for secure hashing. Example:

    $hash = password_hash('password', PASSWORD_DEFAULT);
    

38. What is CSRF and how to prevent it?
    Answer: Cross-Site Request Forgery is an attack where unauthorized actions are performed on behalf of a user. Prevent it with tokens.
39. What is the purpose of openssl_encrypt()?
    Answer: It encrypts data using OpenSSL.
40. How do you handle file uploads securely?
    Answer: Validate file types, use unique names, and store files outside the web root.