PHP interview questions and answers

Comprehensive, community-driven list of essential PHP interview questions. Whether you are a candidate or interviewer, these interview questions will help prepare you for your next PHP interview ahead of time.

  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 T_PAAMAYIM_NEKUDOTAYIM?Its the scope resolution operator (double colon)
  3. What is the cause of this warning: ‘Warning: Cannot modify header information – headers already sent’, and what is a good practice to prevent it?*Cause:* body data was sent, causing headers to be sent too. Prevention: Be sure to execute header specific code first before you output any body data. Be sure you haven’t accidentally sent out whitespace or any other characters.
  4. 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
  5. What is the difference between an interface and an abstract class?An interface defines a contract between an implementing class is and an object that calls the interface. An abstract class pre-defines certain behaviour for classes that will extend it. To a certain degree this can also be considered a contract, since it garantuees certain methods to exist.
  6. What is wrong with classes that predominantly define getters and setters, that map straight to it’s internal members, without actually having methods that execute behaviour?This might be a code smell since the object acts as an ennobled array, without much other use.
  7. 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.
  8. Why is PHP’s implementation of the use of interfaces sub-optimal?PHP doesn’t allow you to define the expected return type of the method’s, which essentially renders interfaces pretty useless.
  9. 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.
  10. 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.
  11. 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 .
  12. How to declare an array in php?Eg : var $arr = array(‘apple’, ‘grape’, ‘lemon’);
  13. 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 ‘);
  14. What is use of in_array() function in php ?in_array used to checks if a value exists in an array
  15. What is use of count() function in php ?count() is used to count all elements in an array, or something in an object
  16. 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.
  17. 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 not hold multiple variables,But 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
  18. How to set cookies in PHP?Setcookie(“sample”, “ram”, time()+3600);
  19. How to Retrieve a Cookie Value?eg : echo $_COOKIE[“user”];
  20. 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’];
  21. what types of loops exist in php?for,while,do while and foreach (NB: You should learn its usage)
  22. How to create a mysql connection?mysql_connect(servername,username,password);
  23. How to select a database?mysql_select_db($db_name);
  24. How to execute an sql query? How to fetch its result ?$my_qry = mysql_query(“SELECT * FROM `users` WHERE `u_id`=’1′; “);
    $result = mysql_fetch_array($my_qry);
    echo $result[‘First_name’];
  25. Write a program using while loop$my_qry = mysql_query(“SELECT * FROM `users` WHERE `u_id`=’1′; “);
    while($result = mysql_fetch_array($my_qry))
    echo $result[‘First_name’.].”<br/>”;
  26. How we can retrieve the data in the result set of MySQL using PHP?
    • 1. mysql_fetch_row
    • 2. mysql_fetch_array
    • 3. mysql_fetch_object
    • 4. mysql_fetch_assoc
  27. What is the use of explode() function ?Syntax : array explode ( string $delimiter , string $string [, int $limit ] );
    This function breaks a string into an array. Each of the array elements is a substring of string formed by splitting it on boundaries formed by the string delimiter.
  28. What is the difference between explode() and split() functions?Split function splits string into array by regular expression. Explode splits a string into array by string.
  29. What is the use of mysql_real_escape_string() function?It is used to escapes special characters in a string for use in an SQL statement
  30. Write down the code for save an uploaded file in php.if ($_FILES[“file”][“error”] == 0)
    “upload/” . $_FILES[“file”][“name”]);
    echo “Stored in: ” . “upload/” . $_FILES[“file”][“name”];
  31. How to create a text file in php?$filename = “/home/user/guest/newfile.txt”;
    $file = fopen( $filename, “w” );
    if( $file == false )
    echo ( “Error in opening new file” );
    fwrite( $file, “This is a simple test\n” );
    fclose( $file );
  32. 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.
  33. 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.
  34. How to redirect a page in php?The following code can be used for it, header(“Location:index.php”);
  35. How stop the execution of a php scrip ?exit() function is used to stop the execution of a page
  36. 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
  37. How to find the length of a string?strlen() function used to find the length of a string
  38. 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.
  39. what is the use of isset() in php?This function is used to determine if a variable is set and is not NULL
  40. What is the difference between mysql_fetch_array() and mysql_fetch_assoc() ?mysql_fetch_assoc function Fetch a result row as an associative array, While mysql_fetch_array() fetches an associative array, a numeric array, or both
  41. What is mean by an associative array?Associative arrays are arrays that use string keys is called associative arrays.
  42. 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.
  43. 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.
  44. 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
  45. 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="MyArray[]" />  <input name="MyArray[]" />  <input name="MyArray[]" />  <input name="MyArray[]" />
  46. Define Object-Oriented MethodologyObject orientation is a software/Web development 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
  47. How do you define a constant?Using define() directive, like define (“MYCONSTANT”,150)
  48. 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 : mail($to,$subject,$message,$headers);
  49. 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.
  50. Difference between mysql_connect and mysql_pconnect? There is a good page in the php manual on the subject, in short mysql_pconnect() makes a persistent connection to the database which means a SQL link that do not close when the execution of your script ends. mysql_connect()provides only for the databasenewconnection while using mysql_pconnect , the function would first try to find a (persistent) link that’s already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection… the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use.
  51. What is the use of “ksort” in php?It is used for sort an array by key in reverse order.
  52. 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.
  53. What are the encryption techniques in PHPMD5 PHP implements the MD5 hash algorithm using the md5 function,
    eg : $encrypted_text = md5 ($msg);

    mcrypt_encrypt :- string mcrypt_encrypt ( string $cipher , string $key , string $data , string $mode [, string $iv ] );
    Encrypts plaintext with given parameters

  54. 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.
  55. How to delete a file from the systemUnlink() deletes the given file from the file system.
  56. How to get the value of current session id?session_id() function returns the session id for the current session.
  57. What are the differences between mysql_fetch_array(), mysql_fetch_object(), mysql_fetch_row()?
    • Mysql_fetch_array Fetch a result row as an associative array, a numeric array, or both.
    • mysql_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
    • mysql_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.
  58. 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.
  59. what is sql injection ?SQL injection is a malicious code injection technique.It exploiting SQL vulnerabilities in Web applications
  60. What is x+ mode in fopen() used for?Read/Write. Creates a new file. Returns FALSE and an error if file already exists
  61. How to find the position of the first occurrence of a substring in a stringstrpos() is used to find the position of the first occurrence of a substring in a string
  62. 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.
  63. 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.
  64. What are the different errors in PHP? In PHP, there are three types of runtime errors, they are:

    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.
    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.

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PHP | MVC | Codeignitor | Zend | Yii | Smarty | Android | Laravel Expert Senior Software Developer.I love my job and feel happy to working on new ideas and technologies.

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