PHP interview questions

Welcome !!!. In this section we are providing you some frequently asked PHP Interview Questions which will help you to win interview session easily. Candidates must read this section,Then by heart the questions and answers.

Also, review sample answers and advice on how to answer these typical interview questions. PHP is an important part of the web world, and every web developer should have the basic knowledge in PHP.Common PHP interview questions, which should help you become a best PHP codder. We hope you find these questions useful. If you are an interviewer, Take the time to read the common interview questions you will most likely be asked. PHP interview questions and answers for experienced

  1. What is PHP?

    PHP is a server side scripting language commonly used for web applications. PHP has many frameworks and cms for creating websites.Even a non technical person can cretae sites using its CMS.WordPress,osCommerce are the famus CMS of php.It is also an object oriented programming language like java,C-sharp etc.It is very eazy for learning

  2. What is the use of "echo" in php?

    It is used to print a data in the webpage, Example: <?php echo 'Car insurance'; ?> , The following code print the text in the webpage

  3. How to include a file to a php page?

    We can include a file using "include() " or "require()" function with file path as its parameter.

  4. What's the difference between include and require?

    If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.

  5. require_once(), require(), include().What is difference between them?

    require() includes and evaluates a specific file, while require_once() does that only if it has not been included before (on the same page). So, require_once() is recommended to use when you want to include a file where you have a lot of functions for example. This way you make sure you don't include the file more times and you will not get the "function re-declared" error.

  6. Differences between GET and POST methods ?

    We can send 1024 bytes using GET method but POST method can transfer large amount of data and POST is the secure method than GET method .

  7. What is the purpose of the superglobal variable called $_SERVER ?

    $_SERVER is an array and it holds the information about paths, headers, and script locations.

  8. How to Detecting request type in PHP ?

    By using $_SERVER['REQUEST_METHOD'] method

  9. How to declare an array in php?

    Eg : var $arr = array('apple', 'grape', 'lemon');

  10. How can PHP interact to Javascript ?

    PHP cannot interact with javascript directly, since php is server side programming language when javascript is a client side programming language. However we can embbed the php variable values to a javascript code section when it complile at the server or javascript can communicate to a php page via http calls

    NB: Javascript can run at the server side as well using Node.js Server

  11. How to manipulate image files using php ?

    GD is library that providing image manipulation capabilities to php, so that we can do so many things such as crop, merge, change grayscale and much more with GD functions

  12. How to manipulate video files using php ?

    There is no inbuilt library available in php, However there are some open source libraries that providing these features

    FFmpeg is a complete, cross-platform solution to record, convert and stream audio and video. We can install this extension in php and use to do variety of tasks

  13. What is cron jobs ?

    Cron jobs are scheduled tasks, executed on regular time intervals set by the developer. They work by running preferred scripts. We can set the time intervals for running these scripts. Its not a part of php compiler, We have several ways to do this based on the platform or the hostign control panel type

  14. How to sent a POST request from php ( Without using any html ) ?

    You could use cURL, that allows you to connect and communicate to many different types of servers with many different types of protocols such as http, https, ftp etc.

  15. How to create a directory if it doesn't already exist ?
    <?php
    if (!file_exists('path/to/directory')) {
        mkdir('path/to/directory', 0777, true);
        }
    ?>
  16. How to delete an element from an array ?

    If you want to just delete a single element you can use unset() or alternatively array_splice().

    unset() method won't change array key when array_splice() method change the array keys automatically

  17. What is the use of 'print' in php?

    This is not actually a real function, It is a language construct. So you can use with out parentheses with its argument list.
    Example print('PHP Interview questions');
    print 'Job Interview ');

  18. What is use of in_array() function in php ?

    in_array used to checks if a value exists in an array

  19. What is use of count() function in php ?

    count() is used to count all elements in an array, or something in an object

  20. What's the difference between include and require?

    It's how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.

  21. What is the difference between Session and Cookie?

    The main difference between sessions and cookies is that sessions are stored on the server, and cookies are stored on the user's computers in the text file format. Cookies can't hold multiple variable while session can hold multiple variables..We can set expiry for a cookie,The session only remains active as long as the browser is open.Users do not have access to the data you stored in Session,Since it is stored in the server.Session is mainly used for login/logout purpose while cookies using for user activity tracking

  22. How to set cookies in PHP?

    Setcookie("sample", "ram", time()+3600);

  23. How to Retrieve a Cookie Value?

    eg : echo $_COOKIE["user"];

  24. How to create a session? How to set a value in session ? How to Remove data from a session?

    Create session : session_start();
    Set value into session : $_SESSION['USER_ID']=1;
    Remove data from a session : unset($_SESSION['USER_ID'];

  25. what types of loops exist in php?

    for,while,do while and foreach (NB: You should learn its usage)

  26. Note:-

    MySQLi (the "i" stands for improved) and PDO (PHP Data Objects) are the MySQL extensions used to connect to the MySQL server in PHP5 or verions, MySQL extension was deprecated in 2012.

    MySQLi only works with MySQL databases whereas PDO will works with 12 other Database systems

    I recommend PDO because, if you want to choose another database instead of MySQL, then you only have to change the connection string and a few queries. But if you are using MySQLi you will need to rewrite the entire code

  27. How to create a mysql connection?
    Example (PDO)
    <?php
    $servername = "localhost";
    $username = "username";
    $password = "password";

    try {
        $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
        // set the PDO error mode to exception
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        echo "Connected successfully";
        }
    catch(PDOException $e)
        {
        echo "Connection failed: " . $e->getMessage();
        }
    ?>

    Example (MySQLi Object-Oriented)
    <?php
    $servername = "localhost";
    $username = "username";
    $password = "password";
    $dbname = "myDB"; // Optional

    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);

    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }
    echo "Connected successfully";
    ?>

    Example (MySQLi Procedural)
    <?php
    $servername = "localhost";
    $username = "username";
    $password = "password";
    $dbname = "myDB"; // Optional


    // Create connection
    $conn = mysqli_connect($servername, $username, $password, $dbname);

    // Check connection
    if (!$conn) {
        die("Connection failed: " . mysqli_connect_error());
    }
    echo "Connected successfully";
    ?>

  28. What are prepared statements?

    A prepared statement or a parameterized statement is a feature used to execute the same SQL queries repeatedly with high efficiency. It consists of two stages: prepare and execute. Prepared statements reduce parsing time because preparation on the query is done only once while the statement is executed multiple times. It is very useful against SQL injections because parameter values won't alter objective of the statement.

  29. How to execute an sql query? How to fetch its result ?
    Example (MySQLi Object-oriented)

    $sql = "SELECT id, firstname, lastname FROM MyGuests";
    $result = $conn->query($sql); // execute sql query

    if ($result->num_rows > 0) {
        // output data of each row
        while($row = $result->fetch_assoc()) { // fetch data from the result set
            echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
        }
    } else {
        echo "0 results";
    }

    Example (MySQLi Procedural)

    $sql = "SELECT id, firstname, lastname FROM MyGuests";
    $result = mysqli_query($conn, $sql); // execute sql query

    if (mysqli_num_rows($result) > 0) {
        // output data of each row
        while($row = mysqli_fetch_assoc($result)) { // fetch data from the result set
            echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
        }
    } else {
        echo "0 results";
    }
    Example (PDO)

    Method 1:USE PDO query method
    $stmt = $db->query('SELECT id FROM Employee');
    $row_count = $stmt->rowCount();
    echo $row_count.' rows selected';

    Method 2: Statements With Parameters
    $stmt = $db->prepare("SELECT id FROM Employee WHERE name=?");
    $stmt->execute(array($name));
    $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
  30. Write a program using while loop
    <?php
    $x = 1;

    while($x <= 5) {
        echo "The number is: $x <br>";
        $x++;
    }
    ?>
  31. How we can retrieve the data in the result set of MySQL using PHP?
    MySQLi methods
    • 1. mysqli_fetch_row
    • 2. mysqli_fetch_array
    • 3. mysqli_fetch_object
    • 4. mysqli_fetch_assoc
    PDO methods
    • 1. PDOStatement::fetch(PDO::FETCH_ASSOC)
    • 2. PDOStatement::fetch(PDO::FETCH_OBJ)
    • 3. PDOStatement::fetch()
    • 4. PDOStatement::fetch(PDO::FETCH_NUM)
  32. What is the use of explode() function ?

    Syntax : array explode ( string $delimiter , string $string [, int $limit ] );
    This function breaks a string into an array. Each of the array elements is a substring of string formed by splitting it on boundaries formed by the string delimiter.

  33. What is the difference between explode() and str_split() functions?

    str_split function splits string into array by regular expression. Explode splits a string into array by string.

  34. What is the use of mysqli_real_escape_string() function?

    It is used to escapes special characters in a string for use in an SQL statement

  35. Write down the code for save an uploaded file in php.
    <?php
    if ($_FILES["file"]["error"] == 0)
    {
    move_uploaded_file($_FILES["file"]["tmp_name"],
          "upload/" . $_FILES["file"]["name"]);
          echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
    }
    ?>
  36. How to create a text file in php?
    <?php
    $filename = "/home/user/guest/newfile.txt";
    $file = fopen( $filename, "w" );
    if( $file == false )
    {
    echo ( "Error in opening new file" ); exit();
    }
    fwrite( $file, "This is a simple test\n" );
    fclose( $file );
    ?>
  37. How to strip whitespace (or other characters) from the beginning and end of a string ?

    The trim() function removes whitespaces or other predefined characters from both sides of a string.

  38. What is the use of header() function in php ?

    The header() function sends a raw HTTP header to a client browser.Remember that this function must be called before sending the actual out put.For example, You do not print any HTML element before using this function.

  39. How to redirect a page in php?

    The following code can be used for it, header("Location:index.php");

  40. How stop the execution of a php scrip ?

    exit() function is used to stop the execution of a page

  41. How to set a page as a home page in a php based site ?

    index.php is the default name of the home page in php based sites

  42. How to find the length of a string?

    strlen() function used to find the length of a string

  43. what is the use of rand() in php?

    It is used to generate random numbers.If called without the arguments it returns a pseudo-random integer between 0 and getrandmax(). If you want a random number between 6 and 12 (inclusive), for example, use rand(6, 12).This function does not generate cryptographically safe values, and should not be used for cryptographic uses. If you want a cryptographically secure value, consider using openssl_random_pseudo_bytes() instead.

  44. what is the use of isset() in php?

    This function is used to determine if a variable is set and is not NULL

  45. What is the difference between mysqli_fetch_array() and mysqli_fetch_assoc() ?

    mysqli_fetch_assoc function Fetch a result row as an associative array, While mysqli_fetch_array() fetches an associative array, a numeric array, or both

  46. What is mean by an associative array?

    Associative arrays are arrays that use string keys is called associative arrays.

  47. What is the importance of "method" attribute in a html form?

    "method" attribute determines how to send the form-data into the server.There are two methods, get and post. The default method is get.This sends the form information by appending it on the URL.Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

  48. What is the importance of "action" attribute in a html form?

    The action attribute determines where to send the form-data in the form submission.

  49. What is the use of "enctype" attribute in a html form?

    The enctype attribute determines how the form-data should be encoded when submitting it to the server. We need to set enctype as "multipart/form-data" when we are using a form for uploading files

  50. How to create an array of a group of items inside an HTML form ?

    We can create input fields with same name for "name" attribute with squire bracket at the end of the name of the name attribute, It passes data as an array to PHP.
    For instance :

    <input name="animal[]" id="cat" />
    <input name="animal[]" id="rat" />
    <input name="animal[]" id="lion" />
    <input name="animal[]" id="snake" />
  51. Define Object-Oriented Methodology

    Object orientation is a software programming methodology that is based on the modeling a real world system.An object is the core concept involved in the object orientation. An object is the copy of the real world enity.An object oriented model is a collection of objects and its inter-relationships

  52. How do you define a constant?

    Using define() directive, like define ("MYCONSTANT",150)

  53. How send email using php?

    To send email using PHP, you use the mail() function.This mail() function accepts 5 parameters as follows (the last 2 are optional). You need webserver, you can't send email from localhost. eg :

    <?php
    mail($to,$subject,$message,$headers);
    ?>
    mcrypt_encrypt :- string mcrypt_encrypt ( string $cipher , string $key , string $data , string $mode [, string $iv ] );
    Encrypts plaintext with given parameters
  54. How to find current date and time?

    The date() function provides you with a means of retrieving the current date and time, applying the format integer parameters indicated in your script to the timestamp provided or the current local time if no timestamp is given. In simplified terms, passing a time parameter is optional - if you don't, the current timestamp will be used.

  55. How to convert one date format into another in PHP ?
    <?php
    $old_date = date('l, F d y h:i:s'); // returns Saturday, January 30 10 02:06:34
    $old_date_timestamp = strtotime($old_date);
    $new_date = date('Y-m-d H:i:s', $old_date_timestamp);
    ?>
  56. What is the use of "ksort" in php?

    It is used for sort an array by key in reverse order.

  57. What is the difference between $var and $$var?

    They are both variables. But $var is a variable with a fixed name. $$var is a variable who's name is stored in $var. For example, if $var contains "message", $$var is the same as $message.

  58. What are the encryption techniques in PHP

    MD5 PHP implements the MD5 hash algorithm using the md5 function,

    <?php
    $encrypted_text = md5 ($msg);
    ?>
  59. What is the use of the function htmlentities?

    htmlentities Convert all applicable characters to HTML entities This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.

  60. How to delete a file from the system

    Unlink() deletes the given file from the file system.

  61. How to get the value of current session id?

    session_id() function returns the session id for the current session.

  62. What are the differences between mysqli_fetch_array(), mysqli_fetch_object(), mysqli_fetch_row()?
    • Mysqli_fetch_array Fetch a result row as an associative array, a numeric array, or both.
    • mysqli_fetch_object ( resource result ) Returns an object with properties that correspond to the fetched row and moves the internal data pointer ahead. Returns an object with properties that correspond to the fetched row, or FALSE if there are no more rows
    • mysqli_fetch_row() fetches one row of data from the result associated with the specified result identifier. The row is returned as an array. Each result column is stored in an array offset, starting at offset 0.
  63. Why we shouldn't use mysql_* functions in PHP?
    • Is not under active development
    • Is officially deprecated as of PHP 5.5 (released June 2013).
    • Has been removed entirely as of PHP 7.0 (released December 2015)
  64. What are the different types of errors in PHP ?

    Here are three basic types of runtime errors in PHP:

    • 1. Notices: These are trivial, non-critical errors that PHP encounters while executing a script - for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all - although you can change this default behavior.
    • 2. Warnings: These are more serious errors - for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.
    • 3. Fatal errors: These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP's default behavior is to display them to the user when they take place.
  65. what is sql injection ?

    SQL injection is a malicious code injection technique.It exploiting SQL vulnerabilities in Web applications

  66. What is x+ mode in fopen() used for?

    Read/Write. Creates a new file. Returns FALSE and an error if file already exists

  67. How to find the position of the first occurrence of a substring in a string

    strpos() is used to find the position of the first occurrence of a substring in a string

  68. What is PEAR?

    PEAR is a framework and distribution system for reusable PHP components.The project seeks to provide a structured library of code, maintain a system for distributing code and for managing code packages, and promote a standard coding style.PEAR is broken into three classes: PEAR Core Components, PEAR Packages, and PECL Packages. The Core Components include the base classes of PEAR and PEAR_Error, along with database, HTTP, logging, and e-mailing functions. The PEAR Packages include functionality providing for authentication, networking, and file system features, as well as tools for working with XML and HTML templates.

  69. Distinguish between urlencode and urldecode?

    This method is best when encode a string to used in a query part of a url. it returns a string in which all non-alphanumeric characters except -_. have replece with a percentege(%) sign . the urldecode->Decodes url to encode string as any %and other symbole are decode by the use of the urldecode() function.

  70. What are the different errors in PHP?

    In PHP, there are three types of runtime errors, they are:

    Warnings:
    These are important errors. Example: When we try to include () file which is not available. These errors are showed to the user by default but they will not result in ending the script.
    Notices:
    These errors are non-critical and trivial errors that come across while executing the script in PHP. Example: trying to gain access the variable which is not defined. These errors are not showed to the users by default even if the default behavior is changed.
    Fatal errors:
    These are critical errors. Example: instantiating an object of a class which does not exist or a non-existent function is called. These errors results in termination of the script immediately and default behavior of PHP is shown to them when they take place. Twelve different error types are used to represent these variations internally.

  71. What is a REST API?

    An API is an interface which can be a program or a web application which is capable to communicate to other websites or programs

    REST stands for REpresentational State Transfer and is an architectural style for exposing your program using existing protocols, typically HTTP

    A REST API utilize HTTP Methods like GET/POST/DELETE/UPDATE etc to get or set data in a server

  72. Give me the list of function you are usually using when you debug your PHP scripts ?

    During the development time, i will put error_reporting(E_ALL); ini_set('display_errors', 1); on the top of the php script to display all the errors and notices.

    I will use print_r, var_dump functions to debug logical errors, there are so many other function also available for the same.