50 PHP interview questions and answers for 2025

byGaurav Dixit (Software Engineer) •
0


Here are 50 PHP interview questions and answers for 2025, covering both basic and advanced concepts:

1. What is PHP?

PHP (Hypertext Preprocessor) is a server-side scripting language designed for web development but also used as a general-purpose programming language.

2. What are the main features of PHP?

  • Open-source
  • Cross-platform compatibility
  • Supports various databases (MySQL, PostgreSQL, MongoDB)
  • Object-oriented programming support
  • Built-in security functions
  • Supports integration with HTML, CSS, JavaScript

3. What is the difference between echo and print?

  • echo can take multiple parameters and does not return a value.
  • print can only take one parameter and returns 1, so it can be used in expressions.

Example:

echo "Hello", " World!"; // Works  
print "Hello"; // Works

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

  • == checks for value equality, ignoring type.
  • === checks for both value and type.

Example:

var_dump(5 == "5");  // true
var_dump(5 === "5"); // false

5. How do you declare a PHP variable?

All PHP variables start with a $ sign, followed by the variable name.

$name = "John";
$age = 30;

6. What is the scope of a variable in PHP?

PHP variables have four types of scope:

  1. Local – Defined within a function
  2. Global – Defined outside a function
  3. Static – Retains value between function calls
  4. Superglobal – $GLOBALS, $_POST, $_GET, etc.

7. How do you create a constant in PHP?

Use define() or const.

define("SITE_NAME", "MyWebsite");  
const API_KEY = "123456";

8. What is the difference between require and include?

  • require throws a fatal error if the file is missing.
  • include throws a warning but continues execution.

Example:

require "file.php"; // Script stops if not found  
include "file.php"; // Script continues even if missing

9. What is the difference between require_once and require?

  • require_once ensures the file is included only once, preventing multiple inclusions.
  • require allows multiple inclusions.

10. How can you connect to a MySQL database in PHP?

Using MySQLi (improved) or PDO.

MySQLi Example:

$conn = new mysqli("localhost", "user", "password", "database");
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

PDO Example:

try {
    $pdo = new PDO("mysql:host=localhost;dbname=test", "user", "password");
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

11. What is the difference between MySQLi and PDO?

  • MySQLi is specific to MySQL, whereas PDO supports multiple databases.
  • PDO uses prepared statements more efficiently.

12. What is a PHP session?

A session stores user-specific information across multiple pages.

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

13. What is a PHP cookie?

Cookies store small data on the user's computer.

setcookie("username", "John", time() + (86400 * 30), "/");

14. What is the difference between isset() and empty()?

  • isset() checks if a variable is declared and not null.
  • empty() checks if a variable is empty (0, "", null, false, array()).

15. What are magic methods in PHP?

Magic methods start with double underscores (__), like __construct(), __destruct(), __get(), __set(), etc.

Example:

class Test {
    function __construct() {
        echo "Object created!";
    }
}
$obj = new Test(); // Outputs: Object created!

16. What is the difference between GET and POST?

Feature GET POST
Visibility Data is visible in the URL Data is hidden
Security Less secure More secure
Data Limit Limited (URL length) No limit
Usage Fetching data Submitting forms

17. What are PHP superglobals?

PHP provides predefined variables, such as:

  • $_GET
  • $_POST
  • $_SESSION
  • $_COOKIE
  • $_SERVER
  • $_FILES

18. How to handle errors in PHP?

Using try...catch.

try {
    $num = 5 / 0;
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

19. What are PHP data types?

  1. String
  2. Integer
  3. Float
  4. Boolean
  5. Array
  6. Object
  7. NULL
  8. Resource

20. How to prevent SQL Injection in PHP?

Use prepared statements.

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?");
$stmt->execute([$email]);

Advanced Questions

21. What is Composer in PHP?

A dependency manager for PHP packages.

22. What is the difference between traits and interfaces?

  • Traits allow multiple inheritance.
  • Interfaces define required methods.

23. What is spl_autoload_register()?

Automatically loads class files without require.

spl_autoload_register(function($class) {
    include $class . ".php";
});

24. What are namespaces in PHP?

Avoids name conflicts.

namespace MyNamespace;
class Test {}

25. What are anonymous functions?

Functions without names.

$greet = function($name) { return "Hello, $name"; };
echo $greet("John");

26. What is the difference between an abstract class and an interface?

Feature Abstract Class Interface
Method Definition Can have both abstract and concrete methods Only method signatures (no implementation)
Variables Can have properties Cannot have properties
Multiple Inheritance No Yes (A class can implement multiple interfaces)
Constructor Yes No

Example:

abstract class Animal {
    abstract public function makeSound();
}
interface CanFly {
    public function fly();
}

27. What is PSR in PHP?

PSR (PHP Standard Recommendations) defines coding standards for PHP projects.
Examples:

  • PSR-1: Basic coding standard
  • PSR-2: Coding style guide
  • PSR-4: Autoloading standard

28. What is Laravel?

Laravel is a PHP framework for web applications, offering:

  • MVC architecture
  • Eloquent ORM
  • Blade templating
  • Authentication & Authorization
  • Artisan CLI

29. What are PHP generators?

Generators return values on demand using yield, saving memory.

function getNumbers() {
    for ($i = 1; $i <= 3; $i++) {
        yield $i;
    }
}
foreach (getNumbers() as $num) {
    echo $num; // 1 2 3
}

30. How to implement caching in PHP?

Using APCu, Redis, or Memcached.
Example with APCu:

apcu_store('key', 'value', 300); // Store for 5 minutes
$value = apcu_fetch('key');

31. How to handle file uploads in PHP?

Use $_FILES.

if ($_FILES["file"]["error"] == 0) {
    move_uploaded_file($_FILES["file"]["tmp_name"], "uploads/" . $_FILES["file"]["name"]);
}

32. What is the difference between REST and SOAP APIs?

Feature REST SOAP
Protocol HTTP, JSON XML-RPC
Simplicity Easy Complex
Speed Faster Slower
State Stateless Stateful

33. What are the different types of errors in PHP?

  1. Parse Error – Syntax errors
  2. Fatal Error – Undefined functions or missing files
  3. Warning – Non-fatal issues
  4. Notice – Minor issues

Example:

error_reporting(E_ALL);
ini_set('display_errors', 1);

34. How does PHP manage memory?

PHP uses Garbage Collection (GC) to free unused memory.

For manual cleanup:

gc_collect_cycles();

35. How to prevent Cross-Site Scripting (XSS) in PHP?

Use htmlspecialchars():

echo htmlspecialchars("<script>alert('Hacked');</script>");

36. What is the difference between explode() and implode()?

  • explode() converts a string to an array.
  • implode() converts an array to a string.

Example:

$arr = explode(",", "apple,banana,grape");
$str = implode("-", $arr);

37. How to use cURL in PHP?

cURL is used for making HTTP requests.

$ch = curl_init("https://api.example.com/data");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

38. What is the difference between foreach and for loop?

  • for is used with index-based arrays.
  • foreach is used with associative arrays and objects.

Example:

$colors = ["Red", "Green", "Blue"];
foreach ($colors as $color) {
    echo $color;
}

39. What are type hinting and strict types in PHP?

Type hinting enforces data types in function arguments.

function add(int $a, int $b): int {
    return $a + $b;
}

Enable strict types at the beginning of a file:

declare(strict_types=1);

40. How to implement CSRF protection in PHP?

Use CSRF tokens in forms:

session_start();
$_SESSION['csrf_token'] = bin2hex(random_bytes(32));

Validate token before form submission.

41. What is a prepared statement in PHP?

A method to prevent SQL injection.

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?");
$stmt->execute([$email]);

42. What is the difference between array_merge() and array_combine()?

  • array_merge() joins two arrays.
  • array_combine() creates an associative array from two arrays.

Example:

$keys = ['name', 'age'];
$values = ['John', 30];
$result = array_combine($keys, $values);

43. How to sort an array in PHP?

sort($arr);  // Ascending
rsort($arr); // Descending
asort($arr); // Ascending associative
ksort($arr); // Sort by key

44. What are lambda functions in PHP?

Anonymous functions assigned to variables.

$sum = function($a, $b) { return $a + $b; };
echo $sum(2, 3);

45. What is the difference between json_encode() and json_decode()?

  • json_encode() converts PHP to JSON.
  • json_decode() converts JSON to PHP.

Example:

$json = json_encode(["name" => "John"]);
$data = json_decode($json, true);

46. What is a singleton class in PHP?

A class that allows only one instance.

class Singleton {
    private static $instance = null;
    private function __construct() {}
    public static function getInstance() {
        if (!self::$instance) self::$instance = new Singleton();
        return self::$instance;
    }
}

47. What is dependency injection in PHP?

A design pattern for managing dependencies.

class Logger {
    public function log($message) { echo $message; }
}
class User {
    private $logger;
    public function __construct(Logger $logger) { $this->logger = $logger; }
}

48. What is array_map() in PHP?

Applies a function to all elements of an array.

$numbers = [1, 2, 3];
$squared = array_map(fn($n) => $n * $n, $numbers);

49. How to send an email using PHP?

Using mail() function:

mail("user@example.com", "Subject", "Message");

Or using PHPMailer for better handling.

50. How to optimize PHP performance?

  • Use opcode caching (OPcache)
  • Optimize database queries
  • Use lazy loading
  • Implement CDN & caching
  • Avoid unnecessary loops
  • Enable compression (Gzip)

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