PHP: Hypertext Preprocessor is open source server-side scripting language that is widely used for creation of dynamic web applications.It was developed by Rasmus Lerdorf also know as Father of PHP in 1994.

PHP is a loosely typed language , we didn’t have to tell PHP which kind of Datatype a Variable is. PHP automatically converts the variable to the correct datatype , depending on its value.

T_PAAMAYIM_NEKUDOTAYIM is scope resolution operator used as :: (double colon) .Basically it used to calling static methods/variables of a Class.

Example usage:-

		
 $Cache::getConfig($key);

In PHP == is equal operator and returns TRUE if $a is equal to $b after type juggling and === is Identical operator and return TRUE if $a is equal to $b, and they are of the same data type.

Example Usages:

<?php 
   $a=true ;
   $b=1;
   // Below condition returns true and prints a and b are equal
   if($a==$b){
    echo "a and b are equal";
   }else{
    echo "a and b are not equal";
   }
   //Below condition returns false and prints a and b are not equal because $a and $b are of  different data types.
   if($a===$b){
    echo "a and b are equal";
   }else{
    echo "a and b are not equal";
   }
?>  
		

As HTTP is state protocol.To maintain states on server and share data across multiple pages PHP session are used.PHP sessions are simple way to store data for individual users/client against a unique session ID.Session IDs are normally sent to the browser via session cookies and the ID is used to retrieve existing session data,if session id is not present on server PHP creates a new session, and generate a new session ID.

Example Usage:-

<?php 
//starting a session
session_start();
//Creating a session 
$_SESSION['user_info']=['user_id'=>1,'first_name'=>'php','last_name'=>'scots','status'=>'active'];

//checking session
if(isset($_SESSION['user_info'])){
echo "logged In";
}

//un setting remove a value from session
unset($_SESSION['user_info']['first_name']);

// destroying complete session
session_destroy();

?>

In PHP 5.3 or below we can register a variable session_register() function.It is deprecated now and we can set directly a value in $_SESSION Global.

Example usage:

<?php
   // Starting session
    session_start();
   // Use of session_register() is deprecated
    $username = "PhpScots";
    session_register("username");
   // Use of $_SESSION is preferred
    $_SESSION["username"] = "PhpScots";
?>


Also Read Laravel interview questions

PHP sessions are stored on server generally in text files in a temp directory of server.
That file is not accessible from outside word. When we create a session PHP create a unique session id that is shared by client by creating cookie on clients browser.That session id is sent by client browser to server each time when a request is made and session is identified.
The default session name is “PHPSESSID”.

Default session time in PHP is 1440 seconds (24 minutes) and Default session storage path is temporary folder/tmp on server.

You can change default session time by using below code

<?php
// server should keep session data for AT LEAST 1 hour
ini_set('session.gc_maxlifetime', 3600);

// each client should remember their session id for EXACTLY 1 hour
session_set_cookie_params(3600);
?>

In PHP all functions starting with __ names are magical functions/methods. Magical methods always lives in a PHP class.The definition of magical function are defined by programmer itself.

Here are list of magic functions available in PHP

__construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __toString(), __invoke(), __set_state(), __clone() and __debugInfo() .

Include :-Include is used to include files more than once in single PHP script.You can include a file as many times you want.

Syntax:- include(“file_name.php”);

Include Once:-Include once include a file only one time in php script.Second attempt to include is ignored.

Syntax:- include_once(“file_name.php”);

Require:-Require is also used to include files more than once in single PHP script.Require generates a Fatal error and halts the script execution,if file is not found on specified location or path.You can require a file as many time you want in a single script.

Syntax:- require(“file_name.php”);

Require Once :-Require once include a file only one time in php script.Second attempt to include is ignored. Require Once also generates a Fatal error and halts the script execution ,if file is not found on specified location or path.

Syntax:- require_once(“file_name.php”);

PHP constructor and a destructor are special type functions which are automatically called when a PHP class object is created and destroyed.

Generally Constructor are used to intializes the private variables for class and Destructors to free the resources created /used by class .

Here is sample class with constructor and destructer in PHP.

<?php
class Foo {
   
    private $name;
    private $link;

    public function __construct($name) {
        $this->name = $name;
    }

    public function setLink(Foo $link){
        $this->link = $link;
    }

    public function __destruct() {
        echo 'Destroying: ', $this->name, PHP_EOL;
    }
}
?>

PHP supports 9 primitive types

4 scalar types:

• integer
• boolean
• float
• string

3 compound types:

• array
• object
• callable

And 2 special types:

• resource
• NULL

Read Zend Framework interview questions

In PHP Type hinting is used to specify the excepted data type of functions argument.
Type hinting is introduced in PHP 5.

Example usage:-

//send Email function argument $email Type hinted of Email Class. It means to call this function you must have to pass an email object otherwise an error is generated.

<?php
function sendEmail (Email $email)
{
  $email->send();
}
?>

The default max execution time for PHP scripts is set to 30 seconds. If a php script runs longer than 30 seconds then PHP stops the script and reports an error.
You can increase the execution time by changing max_execution_time directive in your php.ini file or calling ini_set(‘max_execution_time’, 300); //300 seconds = 5 minutes function at the top of your php script.

In PHP @ is used to suppress error messages.When we add @ before any statement in php then if any runtime error will occur on that line, then the error handled by PHP

There are 13 types of errors in PHP, We have listed all below

• E_ERROR: A fatal error that causes script termination.
• E_WARNING: Run-time warning that does not cause script termination.
• E_PARSE: Compile time parse error.
• E_NOTICE: Run time notice caused due to error in code.
• E_CORE_ERROR: Fatal errors that occur during PHP initial startup.
  (installation)
• E_CORE_WARNING: Warnings that occur during PHP initial startup.
• E_COMPILE_ERROR: Fatal compile-time errors indication problem with script.
• E_USER_ERROR: User-generated error message.
• E_USER_WARNING: User-generated warning message.
• E_USER_NOTICE: User-generated notice message.
• E_STRICT: Run-time notices.
• E_RECOVERABLE_ERROR: Catchable fatal error indicating a dangerous error
• E_ALL: Catches all errors and warnings.

In PHP both functions are used to find the first occurrence of substring in a string except
stristr() is case-insensitive and strstr is case-sensitive,if no match is found then FALSE will be returned.

Sample Usage:

<?php 
$email = ‘abc@xyz.com’;
$hostname = strstr($email, ‘@’);
echo $hostname;
output: @xyz.com
stristr() does the same thing in Case-insensitive manner
?>

//PHP code to process uploaded file and moving it on server

if($_FILES['photo']['name'])
{
	//if no errors...
	if(!$_FILES['file']['error'])
	{
		//now is the time to modify the future file name and validate the file
		$new_file_name = strtolower($_FILES['file']['tmp_name']); //rename file
		if($_FILES['file']['size'] > (1024000)) //can't be larger than 1 MB
		{
			$valid_file = false;
			$message = 'Oops!  Your file\'s size is to large.';
		}
		
		//if the file has passed the test
		if($valid_file)
		{
			//move it to where we want it to be
			move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/'.$new_file_name);
			$message = 'File uploaded successfully.';
		}
	}
	//if there is an error...
	else
	{
		//set that to be the returned message
		$message = 'Something got wrong while uploading file:  '.$_FILES['file']['error'];
	}
}

PHP count function is used to get the length or numbers of elements in array

<?php
// initializing an array in PHP
$array=['a','b','c'];
// Outputs 3 
echo count($array);
?>

You can open a file download dialog in php by setting Content-Disposition in header.

Here is a usage sample:-

// outputting a PDF file
header('Content-type: application/pdf');
// It will be called downloaded.pdf
header('Content-Disposition: attachment; filename="downloaded.pdf"');
// The PDF source is in original.pdf
readfile('original.pdf');

NO, multiple inheritance is not supported by PHP

Code to post JSON Data in a URL using CURL in PHP

$url='http://www.answerguruji';
$jsonData='{"name":"phpScots","email":"phpscots@onlineinterviewquestions.com",'age':36}';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 0);
curl_setopt($ch, CURLOPT_POSTFIELDS, $jsonData);
curl_close($ch);

Defining a Constant in PHP

define('CONSTANT_NAME',value); 

func_get_args() function is used to get number of arguments passed in a PHP function.

Sample Usage:

function foo() {
   return  func_get_args();
}
echo foo(1,5,7,3);//output 4;
echo foo(a,b);//output 2;
echo foo();//output 0;

crypt(),Mcrypt(),hash() are used for encryption in PHP

Unlink: Is used to remove a file from server.
usage:unlink(‘path to file’);

Unset: Is used unset a variable.
usage: unset($var);

Mbstring

Mbstring is an extension used in PHP to handle non-ASCII strings. Mbstring provides multibyte specific string functions that help us to deal with multibyte encodings in PHP. Multibyte character encoding schemes are used to express more than 256 characters in the regular byte-wise coding system. Mbstring is designed to handle Unicode-based encodings such as UTF-8 and UCS-2 and many single-byte encodings for convenience PHP Character Encoding Requirements.

Below are some features of mbstring

1. It handles the character encoding conversion between the possible encoding pairs.
2. Offers automatic encoding conversion between the possible encoding pairs.
3. Supports function overloading feature which enables to add multibyte awareness to regular string functions.
4. Provides multibyte specific string functions that properly detect the beginning or ending of a multibyte character. For example, mb_strlen() and mb_split()

<?php
$tomorrow = mktime(0, 0, 0, date(“m”) , date(“d”)+1, date(“Y”));
$lastmonth = mktime(0, 0, 0, date(“m”)-1, date(“d”), date(“Y”));
echo ($tomorrow-$lastmonth)/86400;
?>

Calculating days between two dates in PHP

<?Php 
$date1 = date('Y-m-d');
$date2 = '2015-10-2';
$days = (strtotime($date1)-strtotime($date2))/(60*60*24);
echo $days;
?>

Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications. XSS enables attackers to inject client-side script into web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls such as the same-origin policy.

Difference between echo and print in PHP

echo in PHP

• echo is language constructs that display strings.
• echo has a void return type.
• echo can take multiple parameters separated by comma.
• echo is slightly faster than print.

Print in PHP

• print is language constructs that display strings.
• print has a return value of 1 so it can be used in expressions.
• print cannot take multiple parameters.
• print is slower than echo.

PHP Namespaces provide a way of grouping related classes, interfaces, functions and constants.

# define namespace and class in namespace
namespace Modules\Admin\;
class CityController {
}

# include the class using namesapce
use Modules\Admin\CityController ;

PHP is a server side scripting language for creating dynamic web pages. There are so many functions available for displaying output in PHP. Here, I will explain some basic functions for displaying output in PHP. The basic functions for displaying output in PHP are as follows:

• print() Function
• echo() Function
• printf() Function
• sprintf() Function
• Var_dump() Function
• print_r() Function

In PHP, one can specify two different submission methods for a form. The method is specified inside a FORM element, using the METHOD attribute. The difference between METHOD=”GET” (the default) and METHOD=”POST” is primarily defined in terms of form data encoding. According to the technical HTML specifications, GET means that form data is to be encoded (by a browser) into a URL while POST means that the form data is to appear within the message body of the HTTP request.

A database provides more flexibility and reliability than does logging to a file. It is easy to run queries on databases and generate statistics than it is for flat files. Writing to a file has more overhead and will cause your code to block or fail in the event that a file is unavailable. Inconsistencies caused by slow replication in AFS may also pose a problem to errors logged to files. If you have access to MySQL, use a database for logs, and when the database is unreachable, have your script automatically send an e-mail to the site administrator.

You can add 301 redirect in PHP by adding below code snippet in your file.

header("HTTP/1.1 301 Moved Permanently"); 
header("Location: /option-a"); 
exit();

You can access standard error stream in PHP by using following code snippet:

$stderr = fwrite("php://stderr");

$stderr = fopen("php://stderr", "w");

$stderr = STDERR;