MNC php interview questions and answers


1) what is session_set_save_handler in PHP? session_set_save_handler() sets the user-level session storage functions which are used for storing and retrieving data associated with a session. This is most useful when a storage method other than those supplied by PHP sessions is preferred. i.e. Storing the session data in a local database.

2) what is garbage collection? default time ? refresh time? Garbage Collection is an automated part of PHP , If the Garbage Collection process runs, it then analyzes any files in the /tmp for any session files that have not been accessed in a certain amount of time and physically deletes them. arbage Collection process only runs in the default session save directory, which is /tmp. If you opt to save your sessions in a different directory, the Garbage Collection process will ignore it. the Garbage Collection process does not differentiate between which sessions belong to whom when run. This is especially important note on shared web servers. If the process is run, it deletes ALL files that have not been accessed in the directory.

There are 3 PHP.ini variables, which deal with the garbage collector: PHP ini  value

name                                          default

session.gc_maxlifetime     1440 seconds or 24 minutes

session.gc_probability      1

session.gc_divisor              100

3) PHP how to know user has read the email? Using Disposition-Notification-To: in mailheader we can get read receipt.

Add the possibility to define a read receipt when sending an email.

It’s quite straightforward, just edit email.php, and add this at vars definitions:

var $readReceipt = null;

And then, at ‘createHeader’ function add:

if (!empty($this->readReceipt)) { $this->__header .= ‘Disposition-Notification-To: ‘ . $this->__formatAddress($this->readReceipt) . $this->_newLine; }

4) Runtime library loading ? without default mysql support, how to run mysql with php?

dl — Loads a PHP extension at runtime int dl ( string $library )

Loads the PHP extension given by the parameter library .

Use extension_loaded() to test whether a given extension is already available or not. This works on both built-in extensions and dynamically loaded ones (either through php.ini or dl()).

bool extension_loaded ( string $name ) — Find out whether an extension is loaded

Warning :This function has been removed from some SAPI’s in PHP 5.3.

5) what is XML-RPC ? XML-RPC is a remote procedure call protocol which uses XML to encode its calls and HTTP as a transport mechanism. An XML-RPC message is an HTTP-POST request. The body of the request is in XML. A procedure executes on the server and the value it returns is also formatted in XML.

6) default session time ? default session time in PHP is 1440 seconds or 24 minutes.

7) default session save path ? Default session save path id temporary folder /tmp

8) What is the difference between htmlentities() and htmlspecialchars()?

htmlspecialchars() – Convert some special characters to HTML entities (Only the most widely used) htmlentities() – Convert ALL special characters to HTML entities

9) how to do session using DB?

bool session_set_save_handler ( callback $open , callback $close , callback $read , callback $write , callback $destroy , callback $gc ) using this function we can store sessions in DB.

PHP has a built-in ability to override its default session handling. The function session_set_save_handler() lets the programmer specify which functions should actually be called when it is time to read or write session information. by overriding the default functions using session_set_save_handler handle we can store session in Db like below example

class SessionManager {

var $life_time;

function SessionManager() {

// Read the maxlifetime setting from PHP $this->life_time = get_cfg_var(“session.gc_maxlifetime”);

// Register this object as the session handler session_set_save_handler( array( &$this, “open” ), array( &$this, “close” ), array( &$this, “read” ), array( &$this, “write”), array( &$this, “destroy”), array( &$this, “gc” ) );

}

function open( $save_path, $session_name ) {

global $sess_save_path;

$sess_save_path = $save_path;

// Don’t need to do anything. Just return TRUE.

return true;

}

function close() {

return true;

}

function read( $id ) {

// Set empty result $data = ”;

// Fetch session data from the selected database

$time = time();

$newid = mysql_real_escape_string($id); $sql = “SELECT `session_data` FROM `sessions` WHERE `session_id` = ‘$newid’ AND `expires` > $time”;

$rs = db_query($sql); $a = db_num_rows($rs);

if($a > 0) { $row = db_fetch_assoc($rs); $data = $row[‘session_data’];

}

return $data;

}

function write( $id, $data ) {

// Build query $time = time() + $this->life_time;

$newid = mysql_real_escape_string($id); $newdata = mysql_real_escape_string($data);

$sql = “REPLACE `sessions` (`session_id`,`session_data`,`expires`) VALUES(‘$newid’, ‘$newdata’, $time)”;

$rs = db_query($sql);

return TRUE;

}

function destroy( $id ) {

// Build query $newid = mysql_real_escape_string($id); $sql = “DELETE FROM `sessions` WHERE `session_id` = ‘$newid'”;

db_query($sql);

return TRUE;

}

function gc() {

// Garbage Collection

// Build DELETE query. Delete all records who have passed the expiration time $sql = ‘DELETE FROM `sessions` WHERE `expires` < UNIX_TIMESTAMP();’;

db_query($sql);

// Always return TRUE return true;

}

}

10) how to track user logged out or not? when user is idle ? By checking the session variable exist or not while loading th page. As the session will exist longer as till browser closes.

The default behaviour for sessions is to keep a session open indefinitely and only to expire a session when the browser is closed. This behaviour can be changed in the php.ini file by altering the line session.cookie_lifetime = 0 to a value in seconds. If you wanted the session to finish in 5 minutes you would set this to session.cookie_lifetime = 300 and restart your httpd server.

11) how to track no of user logged in ? whenever a user logs in track the IP, userID etc..and store it in a DB with a active flag while log out or sesion expire make it inactive. At any time by counting the no: of active records we can get the no: of visitors.

12) in PHP for pdf which library used?

The PDF functions in PHP can create PDF files using the PDFlib library With version 6, PDFlib offers an object-oriented API for PHP 5 in addition to the function-oriented API for PHP 4. There is also the » Panda module.

FPDF is a PHP class which allows to generate PDF files with pure PHP, that is to say without using the PDFlib library. F from FPDF stands for Free: you may use it for any kind of usage and modify it to suit your needs.

FPDF requires no extension (except zlib to activate compression and GD for GIF support) and works with PHP4 and PHP5.

13) for image work which library?

You will need to compile PHP with the GD library of image functions for this to work. GD and PHP may also require other libraries, depending on which image formats you want to work with.

14) what is oops? encapsulation? abstract class? interface?

Object oriented programming language allows concepts such as modularity, encapsulation, polymorphism and inheritance.

Encapsulation passes the message without revealing the exact functional details of the class. It allows only the relevant information to the user without revealing the functional mechanism through which a particular class had functioned.

Abstract class is a template class that contains such things as variable declarations and methods, but cannot contain code for creating new instances. A class that contains one or more methods that are declared but not implemented and defined as abstract. Abstract class: abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.

Interface: Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be define by its implemented class.

15) what is design pattern? singleton pattern?

A design pattern is a general reusable solution to a commonly occurring problem in software design.

The Singleton design pattern allows many parts of a program to share a single resource without having to work out the details of the sharing themselves.

16) what are magic methods?

Magic methods are the members functions that is available to all the instance of class Magic methods always starts with “__”. Eg. __construct All magic methods needs to be declared as public To use magic method they should be defined within the class or program scope Various Magic Methods used in PHP 5 are: __construct() __destruct() __set() __get() __call() __toString() __sleep() __wakeup() __isset() __unset() __autoload() __clone()

17) what is magic quotes? Magic Quotes is a process that automagically escapes incoming data to the PHP script. It’s preferred to code with magic quotes off and to instead escape the data at runtime, as needed. This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 6.0.0. Relying on this feature is highly discouraged.

18) diff b/w php4 & php5 ? In PHP5 1 Implementation of exceptions and exception handling

2. Type hinting which allows you to force the type of a specific argument as object, array or NULL

3. Overloading of methods through the __call function

4. Full constructors and destructors etc through a __constuctor and __destructor function

5. __autoload function for dynamically including certain include files depending on the class you are trying to create.

6 Finality : can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.

7 Interfaces & Abstract Classes

8 Passed by Reference : In PHP4, everything was passed by value, including objects. This has changed in PHP5 — all objects are now passed by reference.

9 An __clone method if you really want to duplicate an object

19) in php4 can you define a class? how to call class in php4? can you create object in php4?

yes you can define class and can call class by creating object of that class. but the diff b/w php4 & php5 is that in php4 everything was passed by value where as in php5 its by reference. And also any value change in reference object changes the actucal value of object also. And one more thing in introduction of __clone object in PHP5 for copying the object.

20) types of error? how to set error settings at run time?

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 behaviour.

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 behaviour is to display them to the user when they take place.

by using ini_set function.

21) what is cross site scripting? SQL injection?

Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications which allow code injection by malicious web users into the web pages viewed by other users. Examples of such code include HTML code and client-side scripts.

SQL injection is a code injection technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed

22) what is outerjoin? inner join?

OUTER JOIN in SQL allows us to retrieve all values in a certain table regardless of whether these values are present in other tables

An inner join requires each record in the two joined tables to have a matching record. An inner join essentially combines the records from two tables (A and B) based on a given join-predicate.

23) what is URL rewriting?

Using URL rewriting we can convert dynamic URl to static URL Static URLs are known to be better than Dynamic URLs because of a number of reasons 1. Static URLs typically Rank better in Search Engines. 2. Search Engines are known to index the content of dynamic pages a lot slower compared to static pages. 3. Static URLs are always more friendlier looking to the End Users.

along with this we can use URL rewriting in adding variables [cookies] to the URL to handle the sessions.

24) what is the major php security hole? how to avoid?

1. Never include, require, or otherwise open a file with a filename based on user input, without thoroughly checking it first. 2. Be careful with eval() Placing user-inputted values into the eval() function can be extremely dangerous. You essentially give the malicious user the ability to execute any command he or she wishes! 3. Be careful when using register_globals = ON It was originally designed to make programming in PHP easier (and that it did), but misuse of it often led to security holes 4. Never run unescaped queries 5. For protected areas, use sessions or validate the login every time. 6. If you don’t want the file contents to be seen, give the file a .php extension.

25) whether PHP supports Microsoft SQL server ? The SQL Server Driver for PHP v1.0 is designed to enable reliable, scalable integration with SQL Server for PHP applications deployed on the Windows platform. The Driver for PHP is a PHP 5 extension that allows the reading and writing of SQL Server data from within PHP scripts. using MSSQL or ODBC modules we can access Microsoft SQL server.

26) what is MVC? why its been used? Model-view-controller (MVC) is an architectural pattern used in software engineering. Successful use of the pattern isolates business logic from user interface considerations, resulting in an application where it is easier to modify either the visual appearance of the application or the underlying business rules without affecting the other. In MVC, the model represents the information (the data) of the application; the view corresponds to elements of the user interface such as text, checkbox items, and so forth; and the controller manages the communication of data and the business rules used to manipulate the data to and from the model.

WHY ITS NEEDED IS 1 Modular separation of function 2 Easier to maintain 3 View-Controller separation means:

A — Tweaking design (HTML) without altering code B — Web design staff can modify UI without understanding code

27) what is framework? how it works? what is advantage?

In general, a framework is a real or conceptual structure intended to serve as a support or guide for the building of something that expands the structure into something useful. Advantages : Consistent Programming Model Direct Support for Security Simplified Development Efforts Easy Application Deployment and Maintenance

28) what is CURL?

CURL means Client URL Library

curl is a command line tool for transferring files with URL syntax, supporting FTP, FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, LDAP, LDAPS and FILE. curl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, kerberos…), file transfer resume, proxy tunneling and a busload of other useful tricks.

CURL allows you to connect and communicate to many different types of servers with many different types of protocols. libcurl currently supports the http, https, ftp, gopher, telnet, dict, file, and ldap protocols. libcurl also supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading (this can also be done with PHP’s ftp extension), HTTP form based upload, proxies, cookies, and user+password authentication.

29) HOW we can transfer files from one server to another server without web forms?

using CURL we can transfer files from one server to another server. ex:

Uploading file

<?php

/* http://localhost/upload.php: print_r($_POST); print_r($_FILES); */

$ch = curl_init();

$data = array(‘name’ => ‘Foo’, ‘file’ => ‘@/home/user/test.png’);

curl_setopt($ch, CURLOPT_URL, ‘http://localhost/upload.php&#8217;);

curl_setopt($ch, CURLOPT_POST, 1); curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

curl_exec($ch); ?>

output:

Array ( [name] => Foo ) Array ( [file] => Array ( [name] => test.png
[type] => image/png [tmp_name] => /tmp/phpcpjNeQ [error] => 0 [size] => 279 )   )  

  30) using CSS can we have a scroll to table? 
No table won't support scrolling of its data. but we can do another workaround like placing a table
 in a DIV  layer and setting the DIV css property to overflow:auto will do the trick.  

  31) how to increase session time in PHP ? 
In php.ini by setting session.gc_maxlifetime and session.cookie_lifetime values
we can change the session time in PHP.   

 32) what is UI? What are the five primary user-interface components?  
 A user interface is a means for human beings to interact with computer-based "tools" and"messages".
One presumed goal is to make the user's experience productive, efficient, pleasing, and humane.
 The primary components of UIs are  a) metaphors (fundamental concepts communicated
 through words, images, sounds, etc.)
b) mental models (structure of data, functions, tasks, roles, jobs, and people in organizations of work
and/or play)
 c) navigation (the process of moving through the mental models)
d) interaction (all input-output sequences and means for conveying feedback)
 e) and appearance (visual, verbal, acoustic, etc.).
33) How can I set a cron and how can I execute it in Unix, Linux, and windows?

Cron is very simply a Linux module that allows you to run commands at predetermined times or intervals.

In Windows, it’s called Scheduled Tasks. The name Cron is in fact derived from the same word from which we get the word chronology, which means order of time.

The easiest way to use crontab is via the crontab command. # crontab This command ‘edits’ the crontab.

Upon employing this command, you will be able to enter the commands that you wish to run.

My version of Linux uses the text editor vi. You can find information on using vi here.

The syntax of this file is very important – if you get it wrong, your crontab will not function properly.

The syntax of the file should be as follows: minutes hours day_of_month month day_of_week command All the variables, with the exception of the command itself, are numerical constants.

In addition to an asterisk (*), which is a wildcard that allows any value, the ranges permitted for each field are as follows: Minutes: 0-59 Hours: 0-23 Day_of_month: 1-31 Month: 1-12 Weekday: 0-6 We can also include multiple values for each entry, simply by separating each value with a comma.

command can be any shell command and, as we will see momentarily, can also be used to execute a Web document such as a PHP file. So, if we want to run a script every Tuesday morning at 8:15 AM, our mycronjob file will contain the following content on a single line: 15 8 * * 2 /path/to/scriptname This all seems simple enough, right? Not so fast! If you try to run a PHP script in this manner, nothing will happen (barring very special configurations that have PHP compiled as an executable, as opposed to an Apache module).

The reason is that, in order for PHP to be parsed, it needs to be passed through Apache. In other words, the page needs to be called via a browser or other means of retrieving Web content.

For our purposes, I’ll assume that your server configuration includes wget, as is the case with most default configurations. To test your configuration, log in to shell.

If you’re using an RPM-based system (e.g. Redhat or Mandrake), type the following: # wget help If you are greeted with a wget package identification, it is installed in your system.

You could execute the PHP by invoking wget on the URL to the page, like so: # wget http://www.example.com/file.php Now, let’s go back to the mailstock.php file we created in the first part of this article.

We saved it in our document root, so it should be accessible via the Internet. Remember that we wanted it to run at 4PM Eastern time, and send you your precious closing bell report? Since I’m located in the Eastern timezone, we can go ahead and set up our crontab to use 4:00, but if you live elsewhere, you might have to compensate for the time difference when setting this value.

This is what my crontab will look like: 0 4 * * 1,2,3,4,5 wget http://www.example.com/mailstock.php

34)Difference b/w OOPS concept in php4 and PHP5 ?

version 4’s object-oriented functionality was rather hobbled. Although the very basic premises of objectoriented programming (OOP) were offered in version 4, several deficiencies existed, including: • An unorthodox object-referencing methodology • No means for setting the scope (public, private, protected, abstract) of fields and methods • No standard convention for naming constructors • Absence of object destructors • Lack of an object-cloning feature • Lack of support for interfaces

35) Difference b/w MyISAM and InnoDB in MySQL?

Ans:

  • The big difference between MySQL Table Type MyISAM and InnoDB is that InnoDB supports transaction
  • InnoDB supports some newer features: Transactions, row-level locking, foreign keys
  • InnoDB is for high volume, high performance
  • use MyISAM if they need speed and InnoDB for data integrity.
  • InnoDB has been designed for maximum performance when processing large data volumes
  • Even though MyISAM is faster than InnoDB
  • InnoDB supports transaction. You can commit and rollback with InnoDB but with MyISAM once you issue a command it’s done
  • MyISAM does not support foreign keys where as InnoDB supports
  • Fully integrated with MySQL Server, the InnoDB storage engine maintains its own buffer pool for caching data and indexes in main memory. InnoDB stores its tables and indexes in a tablespace, which may consist of several files (or raw disk partitions). This is different from, for example, MyISAM tables where each table is stored using separate files. InnoDB tables can be of any size even on operating systems where file size is limited to 2GB.
  • 36) how to set session tiem out at run time or how to extend the session timeout at runtime?

    Ans:

    Sometimes it is necessary to set the default timeout period for PHP. To find out what the default (file-based-sessions) session timeout value on the server is you can view it through a ini_get command:

    // Get the current Session Timeout Value
    $currentTimeoutInSecs = ini_get(’session.gc_maxlifetime’);

    Change the Session Timeout Value

    // Change the session timeout value to 30 minutes
    ini_set(’session.gc_maxlifetime’, 30*60);

    If you have changed the sessions to be placed inside a Database occasionally implementations will specify the expiry manually. You may need to check through the session management class and see if it is getting the session timeout value from the ini configuration or through a method parameter (with default). It may require a little hunting about.

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    39 Responses to “MNC php interview questions and answers”

    1. MNC php interview questions and answers | No Brainer Says:

      January 5, 2009 — good collection sharag ..thanks a lot

    2. Roshan Shahare Says:

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    6. Jaswinder Singh Says:

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    10. asp Says:

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    11. Swapnil Bedekar Says:

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    18. free tutorials Says:

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    21. Neha Says:

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    22. Srijan Mitra Says:

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    23. purvesh Says:

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    24. Bishnoi Balwant Says:

      good yar…….. add some more questions based on oop …

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    26. Shyam Says:

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    27. Rocky Says:

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    28. ARNAB DAS Says:

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    29. mona thakur Says:

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