PHP Interview Questions and Answers

PHP stands for Hypertext Preprocessor. This language is frequently used in server-side scripting for web development, enabling the creation of dynamic and interactive web pages.

PHP is a server-side scripting language that enables dynamic and interactive features, whereas HTML is a markup language that organizes content on the web. PHP runs on the server, whereas HTML runs on the client.

Numerous data types, such as Integer, Float, String, Boolean, Array, Object, NULL, and Resource, are supported by PHP.

There are two ways to send data to the server: GET and POST. GET has a size restriction, appends data to the URL, and is visible to everybody. POST submits data via the HTTP header, providing more security and no size limitations.

A session is a way to store user-specific information on the server temporarily to be available across multiple pages. Session variables hold this information.

The PHP constructor of the mysqli_connect() PDO can be used to establish a connection to a MySQL database.

Cookies are little files that are kept on the user’s computer and are accessible by the server in order to monitor user behavior. They serve many purposes such as tracking and session management.

PEAR (PHP Extension and Application Repository) is a framework and repository for PHP reusable components.

A PHP file can be included in another PHP file using either of these functions. If the file cannot be located, require() will result in a fatal error while include() will merely issue a warning.

SQL Injection can be prevented by using prepared statements, either with the mysqli or PDO extension.

Dependency Injection is a design pattern that allows an object to receive its dependencies from outside rather than creating them internally. This promotes code decoupling, better testability, and separation of concerns.

Design patterns are reusable solutions to common problems in software design. Some common design patterns in PHP are Singleton, Factory, Observer, Strategy, and MVC.

Performance can be improved through caching mechanisms, optimizing database queries, using lazy loading, employing CDNs, and code profiling.

SOLID is an acronym for five principles of object-oriented programming and design: Single Responsibility Principle, Open/Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle. Following these principles makes an application more maintainable, scalable, and robust.

Composer is a dependency manager for PHP that allows you to manage project libraries, autoload your project classes, and fetch the required packages. It uses a composer.json file to manage dependencies.

Horizontal scaling involves adding more machines to the pool of resources, while vertical scaling involves adding more power (CPU, RAM) to an existing machine.

SQL injection can be prevented by using prepared statements, employing ORM frameworks that sanitize SQL queries, and validating user inputs before they are used in SQL queries.

JWT (JSON Web Tokens) is an open standard for securely transmitting information between parties. They are commonly used for authentication and information exchange in PHP APIs.

Middleware are layers that intercept HTTP requests and responses. They act as a bridge between a request and a response, used for logging, authentication, caching, etc.

PHP Generators provide an easy way to implement simple iterators. They allow you to iterate through a set of data without creating an array in memory, improving performance for large datasets.

Session security can be managed by using secure cookies, implementing session timeout, regenerating session IDs, and using built-in PHP functions to handle sessions securely.

These are all techniques to allow a client to receive real-time updates. Long-polling keeps the connection open until the information is available, WebSockets provide a two-way communication channel, and Server-Sent Events is a one-way channel from server to client.

To reverse a string without using strrev(), you can use a loop to iterate through the string from the end to the start, appending each character to a new string.

To print the first n numbers in a Fibonacci series, you can use two variables to hold the last two Fibonacci numbers and a loop to calculate and display the new number.

To flatten a nested array, you could use recursion. If an element is an array, you would call the function again; otherwise, you would add it to a new flat array.

To implement your own array_filter, you can iterate through the given array and apply the callback function to each element. If the callback returns true, keep the element in a new array.

To check if a string is a palindrome, you can compare the original string and its reverse. If they are the same, then it’s a palindrome.

Loop from 1 to 100. For multiples of 3, print “Fizz”, for multiples of 5, print “Buzz”. For multiples of both, print “FizzBuzz”.

To find the missing number in an array from 1 to n+1, sum all numbers from 1 to n+1 and subtract the sum of the numbers in the array.

Merge sort involves dividing the array into halves, sorting them recursively, and then merging them back together in sorted order.

The Singleton pattern ensures that a class has only one instance and provides a way to access it globally. You would use a private constructor and a static method to manage the instance.

A Dependency Injection container manages object creation and injects dependencies when needed. It helps in decoupling components and making the system more maintainable.

To generate a URL slug, you would replace spaces with hyphens, convert all characters to lowercase, and remove special characters.

To remove duplicates from an array, you can iterate through the array and add each item to a new array only if it doesn’t already exist in the new array.

To count the occurrences of a specific value in an array, you can iterate through the array and use a counter variable to keep track.

Type hinting allows you to specify the expected data type for an argument in a function declaration, providing better error handling and readability.

Magic methods start with __ and allow you to perform actions automatically when certain events occur. Examples include __construct(), __destruct(), __call(), and __get().

The @ symbol is an error control operator that suppresses error messages generated by the expression following it.

Pagination can be implemented using SQL’s LIMIT and OFFSET clauses to fetch a specific subset of records and PHP to generate page numbers and navigation.

Lazy loading is a design pattern that delays the loading of an object until its data is actually needed, reducing initial loading time and resources.

Prepared statements are a feature in database management systems that allow the same SQL query structure to be reused, improving security and performance.

Autoloading allows for automatic file inclusion based on namespaces and class names, removing the need for manual include or require statements for every class.

PHP code can be debugged using various tools and methods such as var_dump(), print_r(), error logs, or using IDE features and xDebug.

In logical operations, short-circuit evaluation skips the evaluation of the remaining conditions if the result is already determined.

The extract() function imports variables from an associative array into the current symbol table.