PHP Interview Questions and Answers

What is PHP?
  • PHP is a server-side scripting language designed for web development. It is open-source, widely used for creating dynamic web pages, and supports multiple databases and various web servers.
What are the key features of PHP?
  • Server-side scripting language
  • Cross-platform compatibility
  • Supports object-oriented programming (OOP)
  • Integration with databases like MySQL, PostgreSQL, etc.
  • Ability to handle forms, session management, and cookies
  • Large library of functions and frameworks
What is the difference between `include` and `require` in PHP?
  • include: Includes the specified file, but the script will continue execution even if the file is not found (throws a warning).
  • require: Includes the specified file, and if the file is not found, it will cause a fatal error and stop the script execution.
What is a session in PHP?
  • A session in PHP is a way to store user information across multiple pages. It uses a session ID to identify the user, and this ID is stored either in cookies or the URL. The data persists until the session is destroyed.
What is the difference between `GET` and `POST` methods in PHP?
  • GET: Sends data as part of the URL. It is less secure as data is visible in the browser's address bar and has a limited data size.
  • POST: Sends data as part of the request body. It is more secure than GET and has no size limitation.
What are superglobals in PHP?
  • Superglobals are built-in variables in PHP that are accessible from anywhere in the script. Examples include `$_GET`, `$_POST`, `$_SESSION`, `$_COOKIE`, `$_FILES`, `$_SERVER`, `$_REQUEST`, and `$_ENV`.
What is the purpose of `isset()` function in PHP?
  • The `isset()` function is used to check if a variable is set and is not NULL. It returns `true` if the variable exists and has a value other than NULL.
What is the purpose of `empty()` function in PHP?
  • The `empty()` function is used to check whether a variable is empty. It returns `true` if the variable does not exist, or if its value is empty (e.g., `""`, `0`, `NULL`, `false`, etc.).
What is the `$_FILES` array in PHP?
  • The `$_FILES` array is a superglobal array used to handle file uploads in PHP. It contains information about the uploaded file, such as name, size, type, and temporary location.
What are PHP error levels?
  • PHP has several error levels that define the types of errors that can be encountered:
    • E_ERROR: Fatal run-time errors.
    • E_WARNING: Run-time warnings (non-fatal errors).
    • E_NOTICE: Notices that represent normal but potentially problematic situations.
    • E_DEPRECATED: Notices about deprecated features.
    • E_ALL: All error types.
What is object-oriented programming (OOP) in PHP?
  • Object-Oriented Programming (OOP) in PHP is a programming paradigm based on the concept of objects and classes. It allows for better organization of code, reusability, and the ability to model real-world entities.
What are the key concepts of OOP in PHP?
  • Class: A blueprint for creating objects.
  • Object: An instance of a class.
  • Inheritance: A mechanism that allows a class to inherit properties and methods from another class.
  • Encapsulation: Bundling data (properties) and methods (functions) that operate on the data within one unit, the class.
  • Polymorphism: The ability to use a method or property in different ways based on the context.
  • Abstraction: Hiding the complexity of the system and exposing only the essential parts of it.
What is the difference between `public`, `private`, and `protected` access modifiers in PHP?
  • public: The property or method is accessible from anywhere, inside or outside the class.
  • private: The property or method is only accessible within the class where it is declared.
  • protected: The property or method is accessible within the class and by subclasses (child classes).
What is the use of the `__construct()` method in PHP?
  • The `__construct()` method is a magic method in PHP used to initialize an object when it is created. It is automatically called when a new object is instantiated.
What is the purpose of the `__destruct()` method in PHP?
  • The `__destruct()` method is a magic method in PHP used to clean up when an object is destroyed. It is automatically called when there are no other references to the object.
What is the difference between `echo` and `print` in PHP?
  • echo: It can take multiple arguments and does not return any value.
  • print: It takes one argument and returns a value (1). It is slower than `echo`.
What is a PHP array?
  • A PHP array is a data structure that stores multiple values in a single variable. PHP supports both indexed and associative arrays. Indexed arrays use numeric indexes, while associative arrays use named keys.
What are the different types of arrays in PHP?
  • Indexed Arrays: Arrays with numeric keys (e.g., `$arr = array(1, 2, 3);`).
  • Associative Arrays: Arrays with named keys (e.g., `$arr = array("name" => "John", "age" => 25);`).
  • Multidimensional Arrays: Arrays containing one or more arrays (e.g., `$arr = array(array(1, 2), array(3, 4));`).
What is the `implode()` function in PHP?
  • The `implode()` function is used to join elements of an array into a string. It can take an optional delimiter between the elements.
What is the `explode()` function in PHP?
  • The `explode()` function splits a string into an array based on a specified delimiter.
What is the purpose of the `foreach` loop in PHP?
  • The `foreach` loop in PHP is used to iterate over arrays. It automatically assigns the current array element to a variable during each iteration.
What is the purpose of the `header()` function in PHP?
  • The `header()` function is used to send raw HTTP headers to the browser. It can be used to redirect pages or modify browser behavior, such as setting content type or cache control.
What is the purpose of `session_start()` in PHP?
  • The `session_start()` function initializes a new session or resumes an existing session. It must be called before any output is sent to the browser.
What is the purpose of `str_replace()` in PHP?
  • The `str_replace()` function is used to replace all occurrences of a search string with a replacement string in a given text.
What is the `strlen()` function in PHP?
  • The `strlen()` function returns the length of a string, i.e., the number of characters in the string.
What is the `substr()` function in PHP?
  • The `substr()` function returns a portion of a string, starting from a specified position and optionally with a specified length.
What is the `strpos()` function in PHP?
  • The `strpos()` function returns the position of the first occurrence of a substring within a string. It returns `false` if the substring is not found.
What is `json_encode()` and `json_decode()` in PHP?
  • json_encode(): Converts a PHP variable into a JSON-encoded string.
  • json_decode(): Converts a JSON string into a PHP variable.
What is the `filter_var()` function in PHP?
  • The `filter_var()` function is used to filter a variable with a specified filter, such as validating email addresses, URLs, and sanitizing input data.
What is the `__autoload()` function in PHP?
  • The `__autoload()` function is a magic function that is automatically called when an attempt is made to use a class that has not been defined. It allows you to load class files dynamically.
What is the `mysqli` extension in PHP?
  • The `mysqli` extension provides a way to interact with MySQL databases. It offers support for prepared statements, transactions, and multiple result sets.
What is the PDO extension in PHP?
  • The PDO (PHP Data Objects) extension provides a consistent interface for accessing different databases. It supports prepared statements, transactions, and error handling.
What is the difference between `mysqli` and `PDO` in PHP?
  • mysqli: Specific to MySQL databases and supports both procedural and object-oriented programming.
  • PDO: A database-agnostic extension that works with multiple databases like MySQL, PostgreSQL, SQLite, etc., and uses an object-oriented approach.
What are PHP magic methods?
  • PHP magic methods are predefined methods in PHP classes that are automatically called in certain situations. Examples include `__construct()`, `__destruct()`, `__get()`, `__set()`, `__call()`, and others.
What is `$_SERVER` in PHP?
  • `$_SERVER` is a PHP superglobal that contains information about the server environment and HTTP headers, such as server name, request method, client IP address, and user agent.
What is the difference between `==` and `===` in PHP?
  • ==: Compares values for equality but ignores type (type coercion). If the values are equal, it returns `true`.
  • ===: Compares both values and types. It returns `true` only if both value and type are identical.
What is the purpose of `die()` and `exit()` in PHP?
  • die(): Terminates the current script. It is equivalent to `exit()`. Optionally, it can print a message before exiting.
  • exit(): Terminates the current script. It can also optionally take a message or a status code.
What is the use of `filter_var()` in PHP?
  • The `filter_var()` function is used to validate and sanitize data. For example, it can validate an email address or URL or sanitize an input string.
What is the difference between `include_once` and `require_once` in PHP?
  • include_once: Includes the specified file only once. If the file has already been included, it will not be included again.
  • require_once: Works the same way as `include_once`, but if the file is not found, it will produce a fatal error, stopping script execution.
What is the use of `setcookie()` in PHP?
  • The `setcookie()` function is used to send a cookie to the client's browser. It can store key-value pairs that can be accessed in subsequent requests.
What is the difference between `is_null()` and `isset()` in PHP?
  • is_null(): Checks if a variable is `NULL`.
  • isset(): Checks if a variable is set and is not `NULL`.
What is the `include()` function in PHP?
  • The `include()` function is used to include and evaluate a specified file. If the file cannot be found, it will generate a warning, but the script will continue execution.
How do you prevent SQL injection in PHP?
  • SQL injection can be prevented by using prepared statements with bound parameters or using ORM libraries that automatically handle SQL escaping and sanitization.
What is a trait in PHP?
  • A trait in PHP is a mechanism for code reuse in single inheritance languages like PHP. It allows methods to be shared across multiple classes without using inheritance.
What is the purpose of `get_class()` function in PHP?
  • The `get_class()` function returns the name of the class of an object or a class itself if passed a string.
What is the `count()` function in PHP?
  • The `count()` function is used to count the number of elements in an array or properties in an object.
What is the `array_map()` function in PHP?
  • The `array_map()` function applies a callback function to the elements of an array, returning a new array with modified elements.
What is the purpose of `array_merge()` in PHP?
  • The `array_merge()` function is used to merge two or more arrays into one array. It appends the elements of the second array to the first array.
What is the `var_dump()` function in PHP?
  • The `var_dump()` function displays the data type and value of a variable. It is useful for debugging and inspecting variable contents.
What are the types of error reporting in PHP?
  • The types of error reporting in PHP include:
    • None: No error reporting.
    • Basic: Reports only major errors.
    • Verbose: Reports all errors, including warnings and notices.
What is the `exit()` function in PHP?
  • The `exit()` function is used to terminate the current script. Optionally, a status code or message can be passed.
How can you send an email in PHP?
  • The `mail()` function is used to send emails in PHP. It requires parameters like the recipient's address, subject, message, and headers.
What is the `mysql_fetch_assoc()` function?
  • The `mysql_fetch_assoc()` function retrieves a result row as an associative array. It returns the row in a format where the field names are the keys.
What are `magic constants` in PHP?
  • Magic constants are predefined constants in PHP that change depending on their context. Examples include `__FILE__`, `__LINE__`, `__CLASS__`, and `__DIR__`.
What is the `implode()` function in PHP?
  • The `implode()` function joins elements of an array into a string using a specified delimiter.
What is the `explode()` function in PHP?
  • The `explode()` function splits a string into an array using a specified delimiter.
What is a `namespace` in PHP?
  • A namespace in PHP is a way to encapsulate code and avoid name collisions between classes, interfaces, and functions.
What is `PDOException` in PHP?
  • `PDOException` is a built-in exception class in PHP used for error handling with PDO (PHP Data Objects). It is thrown when a PDO operation fails.
What is the `$_POST` array in PHP?
  • The `$_POST` superglobal is used to collect form data sent via the HTTP POST method. It contains variables sent by the user from a form.
What are the different types of loops in PHP?
  • The different types of loops in PHP are:
    • for: A basic loop used for a specific number of iterations.
    • while: A loop that runs as long as a condition is true.
    • do-while: A loop that executes at least once and continues while the condition is true.
    • foreach: A loop specifically used to iterate over arrays.