PHP MCQ Questions

The 'u' modifier in PCRE patterns treats pattern and subject as UTF-8 strings. Enables proper matching of multibyte Unicode characters. Without it, regex operates on bytes. Example: /pattern/u. Essential for international character support. Prevents incorrect matches with non-ASCII characters. Use when working with Unicode text.

The convert_uuencode() and convert_uudecode() functions encode/decode using uuencode. Historical encoding for binary data in text. Rarely used in modern applications - base64 preferred.

The defined() function checks if constant exists. Returns boolean. Syntax: defined('CONSTANT_NAME'). Useful before accessing constants or conditional constant definition. Works with both define() and const constants.

The in_array() function searches array for value. Returns boolean. Syntax: in_array($value, $array, $strict). Strict parameter enables type checking. Use for membership tests, validation, or checking allowed values.

The trim() function removes whitespace from string beginning and end. ltrim() removes from left only, rtrim() from right only. Optional parameter specifies characters to remove. Essential for cleaning user input and normalizing data.

Output: Array([\0Foo\0foo]=>1 [\0*\0bar]=>2 [test]=>3). Casting object to array converts properties. Private properties prefixed with \0ClassName\0, protected with \0*\0, public unchanged. Shows internal representation. \0 represents NULL character. Demonstrates property visibility in array casting. Useful for debugging but not typical usage.

n1 = 8 (first 'Foo' position). n2 = 0 (case-insensitive /Foo/i matches 'foo' at start). Tests search() vs regex.

The DivisionByZeroError class thrown when dividing by zero in intdiv() function. Regular division by zero returns INF or NAN, not error. Understanding this distinction prevents confusion.

Output: Warning or Notice about division by zero, then prints INF (infinity). Exception not caught as division by zero doesn't throw Exception, just generates warning.

The bindValue() method binds value to prepared statement parameter at binding time. Unlike bindParam(), later variable changes don't affect statement. Syntax: $stmt->bindValue(':name', $value, PDO::PARAM_TYPE). Use for one-time execution.

The SplPriorityQueue class implements priority queue where elements extracted by priority. Useful for task scheduling or priority-based processing.

The get_include_path() function returns include path string. set_include_path() modifies it. Include path determines where PHP searches for included files. Understanding include path helps troubleshoot file inclusion issues.

The PDO constructor creates database connection. Syntax: new PDO($dsn, $user, $password, $options). DSN specifies database type and connection details. Set PDO::ATTR_ERRMODE to PDO::ERRMODE_EXCEPTION for exception-based error handling. Supports multiple database systems.

Output: session encoded string like 'logged_in|b:1;name|s:4:"Jane";level|i:4;'. Shows serialized session data. session_encode() serializes $_SESSION.

PHP error severity levels: E_ERROR (fatal runtime errors), E_WARNING (non-fatal warnings), E_PARSE (compile-time parse errors), E_NOTICE (runtime notices), E_STRICT (coding standard suggestions), E_DEPRECATED (deprecated feature warnings), E_USER_ERROR/WARNING/NOTICE (user-triggered equivalents), E_ALL (all errors and warnings). Control with error_reporting().

The query() method executes SQL and returns result set as PDOStatement. Syntax: $stmt = $pdo->query($sql). Simpler than prepare/execute for queries without parameters. Returns false on error. Vulnerable to injection without parameters.

The jdtogregorian(), jdtojulian(), jdtojewish(), jdtofrench() functions convert Julian Day to various calendar systems. Enable working with multiple calendar systems in single application.

The errorCode() method returns SQLSTATE error code from last operation. Syntax: $pdo->errorCode(). Returns string error code or NULL if no error. Less detailed than errorInfo() but sufficient for basic error checking.

Features not supported in PHP depend on options, but might include: multiple inheritance (supports single inheritance only), operator overloading (limited), threading (not natively supported), or certain data types from other languages. PHP supports single inheritance, interfaces, traits, but not multiple class inheritance. Tests language limitation knowledge.

The code has XML parsing logic. Without seeing full XML structure and expected output, output depends on XML structure and foreach logic. Tests SimpleXML parsing.

The serialize() function converts PHP values to storable string representations preserving type. unserialize() reverses the process. Useful for session storage and caching. Be cautious with user input to prevent object injection.

The recommendation is to omit the closing PHP tag (?>) at the end of files containing only PHP code. This prevents accidental whitespace after the tag from causing header issues. Closing tags are required only in files mixing PHP and HTML. This practice avoids 'headers already sent' errors.

The setFetchMode() method sets default fetch mode for statement. Syntax: $stmt->setFetchMode(PDO::FETCH_ASSOC). Modes include FETCH_ASSOC, FETCH_OBJ, FETCH_NUM. Applies to all fetch() calls on statement.

The list() construct can now use shorthand syntax [...] in PHP 7.1+. Both work identically: list($a, $b) = $array and [$a, $b] = $array. The bracket syntax is more consistent with modern PHP syntax conventions.

The array_flip() function exchanges array keys with their values - values become keys and vice versa. If multiple values are identical, later occurrence overwrites. Original array remains unchanged. Useful for reversing key-value mappings or creating efficient lookup tables from value lists.

The output depends on understanding pass-by-reference. The function receives reference to $beebar (using &), multiplies it by 2, modifying the original variable, then returns the value. If called with $x=5, after luckyA($x), $x becomes 10 and function returns 10. Reference passing enables functions to modify original variables directly.

The array_column() function extracts single column from multi-dimensional array. Can optionally use another column as keys. Syntax: array_column($array, 'column', 'index_column'). Simplifies extracting specific fields from database results or API responses without loops.

Output: nothing. Strict === requires same type. 10 (int) !== '10' (string). No output as condition false. Tests type comparison.

The sscanf() function parses string according to format extracting values. Opposite of sprintf(). Syntax: sscanf($string, $format, ...$vars). Useful for parsing formatted text into variables.

The array_column() function extracts a single column from multidimensional array, returning array of values from that column. Syntax: array_column($array, 'column_name', 'index_key'). Introduced in PHP 5.5, it simplifies extracting specific fields from arrays of records, like database results or API responses, without manual loops.

The addslashes() function escapes quotes with backslashes. Originally for database escaping but deprecated for that purpose. Use prepared statements instead. stripslashes() reverses. Mainly historical relevance - modern code uses better methods.

The static keyword declares class members belonging to class rather than instances. Accessed via ClassName::$property or ClassName::method(). Static members share one copy across all instances. Use self:: or static:: for late static binding. Useful for utility functions, counters, or shared state.

Output: 400+10 (string concatenation). Dot operator concatenates. Use + for math: $foo + $bar = 410. Tests concatenation vs addition.

Output: 1\nfirst\n3\nsecond\nHello PHP Example\n. First try: myFun(3) returns 3/3=1, outputs '1\n', finally outputs 'first\n'. Second try: myFun(1) returns 3/1=3, outputs '3\n', finally outputs 'second\n'. Then outputs 'Hello PHP Example\n'. Finally blocks always execute after try-catch.

The php_strip_whitespace() function returns PHP code with comments and whitespace removed. Reduces file size while maintaining functionality. Useful for code minification or generating compact code for transmission.

Constructor property promotion (PHP 8.0+) declares and initializes properties in constructor signature: function __construct(public string $name, private int $age). Reduces boilerplate code significantly for simple property initialization.

Output: 62. $$a is variable variable. $a='b' means $$a is $b. $b=22, so $$a+40 = 22+40 = 62. Tests variable variables.

A class is blueprint/template defining properties and methods for objects. Declared with class keyword. Enables OOP: encapsulation, inheritance, polymorphism. Objects are class instances.