PHP Interview Questions and Answers

PHP earlier stood for Personal Home Pages, but now it stands for Hypertext Pre-processor. PHP is a server-side scripting language that is used for building web pages and applications. This language includes many Frameworks and CMS for creating large websites.

Even a non-technical person can create web pages or apps using PHP CMS. PHP Supports various CMS like WordPress, Joomla, Drupal and Frameworks like Laravel, CakePHP, Symfony, etc

• Open source
• Robust functions
• Centralized built-in database
• Extensive community support

PHP was developed by Rasmus Lerdorf in 1994.

PHP 7.4 is the latest version of PHP and 8.0 is the newest version of Mysql.

unlink() : It is used to delete a file.

unset() : It is used to unset a file.

Primarily PHP supports four types of errors, listed below:-

• Syntax Error
• Fatal Error
• Warning Error
• Notice Error

1. Syntax Error: It will occur if there is a syntax mistake in the script

2. Fatal Error: It will happen if PHP does not understand what you have written. For example, you are calling a function, but that function does not exist. Fatal errors stop the execution of the script.

3. Warning Error: It will occur in following cases to include a missing file or using the incorrect number of parameters in a function.

4. Notice Error: It will happen when we try to access the undefined variable.

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If we used $_SERVER[‘REMOTE_ADDR’] to get an IP address, but sometimes it will not return the correct value. If the client is connected with the Internet through Proxy Server then $_SERVER[‘REMOTE_ADDR’] in PHP, it returns the IP address of the proxy server not of the user’s machine.

So here is a simple function in PHP to find the real IP address of the user’s machine.

require() and require_once() both are used for include PHP files into another PHP files. But the difference is with the help of require() we can include the same file many times in a single page, but in case of require_once() we can call the same file many times, but PHP includes that file only single time.

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These both methods are based on the HTTP method.

With the help of define(), we can make constants in PHP.

In PHP array() are the beneficial and essential thing. It allows to access and manipulate with array elements.

List of array() functions in PHP

• array()
• count()
• array_flip()
• array_key_exists()
• array_merge()
• array_pop()
• array_push()
• array_unique()
• implode()
• explode()
• in_array()

PHP has lots of string function that helps in development. Here are some PHP string functions.

• nl2br()
• trim()
• str_replace()
• str_word_count()
• strlen()
• strpos()
• strstr()
• strtolower()
• strtoupper()

For file upload in PHP make sure that the form uses method="post" and attribute: enctype="multipart/form-data". It specifies that which content-type to use when submitting the form.

Session and Cookies both functions are used to store information. But the main difference between a session and a cookie is that in case of session data is stored on the server but cookies stored data on the browsers.

Sessions are more secure than cookies because session stored information on servers. We can also turn off Cookies from the browser.

In PHP header() is used to send a raw HTTP header. It must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP

Example :

header(string,replace,http_response_code);

1. string: It is the required parameters. It specifies the header string to send.

2. replace: It is optional. It indicates whether the header should replace previous or add a second header.

3. http_response_code : It is optional. It forces the HTTP response code to the specified value

PHP has multiple functions to handle files operations like read, write, create or delete a file or file contents.

1. file_put_contents():It is used to create a new file.

Syntax :

file_put_contents(file_name, contentstring, flag)

If file_name doesn't exist, the file is created with the contentstring content. Else, the existing file is override, unless the FILE_APPEND flag is set.

2. file_get_contents(): It is used to read the contents of a text file.

file_get_contents($filename);

With the heal of the header(), we can redirect from one page to another in PHP.

Syntax :

header('location:index.php');

HTML forms provide three methods of encoding.

• application/x-www-form-urlencoded (the default)
• multipart/form-data
• text/plain

multipart/form-data

This is used to upload files to the server. It means no characters will be encoded. So It is used when a form requires binary data, like the contents of a file, to be uploaded.

The .htaccess file is a type of configuration file for use on web servers running the Apache Web Server software. It is used to alter the configuration of our Apache Server software to enable or disable additional functionality that the Apache Web Server software has to offer.

In PHP comments are two types.

1. Single line comments
2. Multi line comments

1. Single line comments: It is used comments a single line of code. It disables a line of PHP code. You have to add // or # before the system.

2. Multi line comments: It is used to comment large blocks of code or writing multiple line comments. You have to add /* before and */ after the system.

1. array_combine(): It is used to creates a new array by using the key of one array as keys and using the value of another array as values.

Example :

$array1 = array('key1', 'key2', 'key3'); $array2 = array(('umesh', 'sonu', 'deepak'); $new_array = array_combine($array1, $array2); print_r($new_array);

OUTPUT : Array([key1]  => umesh[key2]    => sonu[key2]    =>deepak)

2. array_merge(): It merges one or more than one array such that the value of one array appended at the end of the first array. If the arrays have the same strings key, then the next value overrides the previous value for that key.

Example :

$array1 = array("one" => "java","two" => "sql"); $array2 = array("one" => "php","three" => "html","four"=>"Me"); $result = array_merge($array1, $array2); print_r($result); Array ( [one] => php [two] => sql [three] => html [four] => Me )

We can use the count() or size() function to get the number of elements or values in an array in PHP.

PHP has three access modifiers such as public, private, and protected.

• public scope of this variable or function is available from anywhere, other classes, and instances of the object.
• private scope of this variable or function is available in its class only.
• protected scope of this variable or function is available in all classes that extend the current class including the parent class.

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explode() function breaks a string into an array, but the implode() function returns a series from the elements of an array.

Example :
$arr = array("1","2","3","4","5");

$str = implode("-",$arr);

OUTPUT

1-2-3-4-5

$array2 = "My name is umesh";

$a = explode(" ",$array2 );

print_r ($a);

OUTPUT

$a = Array ("My", "name", "is", "umesh");

We need to add validation rules while making web forms. It is used because we need to take inputs from the user in the right way like we need the right email address in the email input field. Some time user did not enter the correct address as we aspect. That's why we need validation.

Validations can be applied on the server side or the client side.

Server Side Validation

In the Server Side Validation, the input submitted by the user is being sent to the server and validated using one of the server-side scripting languages like ASP.Net, PHP, etc.

Client Side Validation

In the Client Side Validation, we can provide a better user experience by responding quickly at the browser level.

A cookie is a small file that stores on user's browsers. It is used to store users information. We can create and retrieve cookie values in PHP.

A cookie can be created with the setcookie() function in PHP.

These both are PHP inbuilt function which is used to open & close a file which is pointed file pointer.

There are differences between php5 and php7.

• PHP 5 is released 28 August 2014 but PHP 7 released on 3 December 2015
• It is one of the advantages of the new PHP 7 is the compelling improvement of performance.
• Improved Error Handling
• Supports 64-bit windows systems
• Anonymous Class
• New Operators

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mysql_insert_id() is used to get last insert id. It is used after insert data query. It will work when id is enabled as AUTO INCREMENT

With the help of strip_tags(), we can remove HTML tags from data in PHP.

The strip_tags() function strips a string from HTML, XML, and PHP tags.

strip_tags(string,allow)

The first parameter is required. It specifies the string to check.

The second parameter is optional. It specifies allowable tags. Mention tags will not be removed

It is used to replaces some characters with some other characters in a string.

Suppose, we want to Replace the characters "Umesh" in the string "Umesh Singh" with "Sonu"

echo str_replace("Umesh","Sonu","Umesh Singh");

It is used to extract a part of the string. It allows three parameters or arguments out of which two are mandatory, and one is optional

echo substr("Hello world",6);

It will return first six characters from a given string.

It is used to dump information about one or more variables. It displays structured data such as the type and value of the given variable.

Example:

$var_name1=12; int(12);

It is used to inserts HTML line breaks ( <br /> or <br /> ) in front of each newline (\n) in a string.

$$var is known as reference variable where $var is a normal variable.

1. isset(): It returns TRUE if the variable exists and has a value other than NULL. It means variables assigned a "", 0, "0", or FALSE are set.

2. empty(): It checks to see if a variable is empty. It interpreted as: "" (an empty string).

isset($var) && !empty($var)

will be equals to !empty($var)

1. mysql_fetch_object: It returns the result from the database as objects. In this field can be accessed as $result->name

2. mysql_fetch_array: It returns result as an array. In this field can be accessed as $result->[name]

Constructor and a Destructor both are special functions which are automatically called when an object is created and destroyed.

$actual_link = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") . "://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";

For including a file into another PHP file we can use various function like include(), include_once(), require(), require_once().

The items of an array can be sorted by various methods.

• sort() - it sort arrays in ascending order
• rsort() - it sort arrays in descending order
• asort() - it sorts associative arrays in ascending order, according to the value
• ksort() - it sort associative arrays in ascending order, according to the key
• arsort() - it sorts associative arrays in descending order, according to the value
• krsort() - it sorts associative arrays in descending order, according to the key

The error_reporting() function defines which errors are reported.We can modify these errors in php.ini. You can use these given function directly in php file.

error_reporting(E_ALL);
ini_set('display_errors', '1');

Magic methods are unique names, starts with two underscores, which denote means which will be triggered in response to particular PHP events.

The magic methods available in PHP are given below:-

• __construct()
• __destruct()
• __call()
• __get()
• __unset()
• __autoload()
• __set()
• __isset()

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A trait is a group of various methods that reuse in single inheritance. A Trait is intended to reduce some limitations of single inheritance by enabling a developer to reuse sets of processes. We can combine traits and classes to reduce complexity, avoid problems typically associated with Mixins and multiple inheritances.

Inheritance has three types, are given below.

• Single inheritance
• Multiple inheritance
• Multilevel inheritance

But PHP supports only single inheritance, where only one class can be derived from a single parent class. We can do the same thing as multiple inheritances by using interfaces.

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We can do it by various methods, If you have allow_url_fopen set to true:

• We can download images or files from an external server  with cURL() But in this case, curl has been enabled on both servers
• We can also do it by file_put_contents()

• InnoDB
• CSV
• MEMORY
• ARCHIVE
• MyISAM

With PHP 5.6+ "InnoDB" is treated by default database storage engine. Before that MyISAM defaulted storage engine.

These all are PHP Operators.

• = is used to assign value in variables. It is also called assignments operators.
• == is used to check if the benefits of the two operands are equal or not.
• === is used checks the values as well as its data type.

We can define a class with keyword "class" followed by the name of the class.

Example :

class phpClass {
    public function test() {
       echo 'Test';
    }
}

Its properties cannot be declared final, only classes and methods may be declared as final. If the class or method defined as final, then it cannot be extended.

You can use this SELECT MAX(salary) FROM employee WHERE Salary NOT IN ( SELECT Max(Salary) FROM employee); Query to find the 2nd highest salary of the employee.

It is used with the SELECT statement to restrict the number of rows in the result set. Limit accepts one or two arguments which are offset and count.

The syntax of limit is a

SELECT name, salary FROM employee LIMIT 1, 2

COUNT(*) is used to count the number of rows in the table.

SELECT COUNT(*) FROM BestPageTable;

MVC is an application in PHP which separates the application data and model from the view.

The full form of MVC is Model, View & Controller. The controller is used to interacting between the models and views.

Example: Laravel, YII, etc

It is an application package manager for the PHP programming language that provides a standard format for managing dependencies of PHP software. The composer is developed by Nils Adermann and Jordi Boggiano, who continue to lead the project. The composer is easy to use, and installation can be done through the command line.

It can be directly downloaded from https://getcomposer.org/download

Using the composer can solve the following problems:

• Resolution of dependency for PHP packages
• To keep all packages updated
• The solution is autoloading for PHP packages.

It is used to get the name and path of current page/file.

It suppresses error messages. It’s not a good habit to use @ because it can cause massive debugging headaches because it will even contain critical errors

Namespace allows us to use the same function or class name in different parts of the same program without causing a name collision.

With the help of $_SERVER['HTTP_USER_AGENT']

It is a PHP library and a command line tool that helps us to send files and also download data over HTTP and FTP. It also supports proxies, and you can transfer data over SSL connections.

$num = 12345;
$revnum = 0;
while ($num > 1)
{
$rem = $num % 10;
$revnum = ($revnum * 10) + $rem;
$num = ($num / 10);
}

echo "Reverse number of 12345 is: $revnum";

Many differences occur between the interface and abstract class in php.

• Abstract methods can declare with protected, public, private. But in case of Interface methods stated with the public.
• Abstract classes can have method stubs, constants, members, and defined processes, but interfaces can only have constants and methods stubs.
• Abstract classes do not support multiple inheritance but interface support this.
• Abstract classes can contain constructors, but the interface does not support constructors.

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The aggregate function performs a calculation on a set of values and returns a single value. It ignores NULL values when it performs calculation except for the COUNT function.

MySQL provides various aggregate functions that include AVG(), COUNT(), SUM(), MIN(), MAX().

There are lots of differences between storage engines. Some are given below:-

• MyISAM supports Table-level Locking, but InnoDB supports Row-level Locking
• MyISAM designed for the need of speed but InnoDB designed for maximum performance when processing a high volume of data
• MyISAM does not support foreign keys, but InnoDB supports foreign keys
• MyISAM supports full-text search, but InnoDB does not support this
• MyISAM does not support the transaction, but InnoDB supports transaction
• You cannot commit and rollback with MyISAM, but You can determine and rollback with InnoDB
• MyISAM stores its data, tables, and indexes in disk space using separate three different files, but InnoDB stores its indexes and tables in a tablespace

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An SQL injection is a code injection malpractice or technique used to inject and execute malicious SQL statements to attack data-driven applications. It exploits the security vulnerability present in an application's software.

Place this code in your htaccess file.

RewriteEngine On

RewriteCond %{HTTPS} on

RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

Apache HTTP server is the most popular open source web server. Apache has been in use since the year 1995. It powers more websites than any other product.

Both used to deploy your Java Servlets and JSPs. Apache is an HTTP Server, serving HTTP. Tomcat is a Servlet and JSP Server serving Java technologies.

• Sending mail using the PHP mail function with minimum parameters we tend to should use headers like MIME-version, Content-type, reply address, from address, etc. to avoid this case
• Did not use correct SMTP mail script like PHPmailer.
• Should not use website link in mail content.

It stands for PHP Extension and Application Repository. It is that the next revolution in PHP. It is used to install packages automatically.

• SOAP represent for Simple Object Access Protocol, and REST stands for Representation State Transfer.
• SOAP is a protocol and Rest is an architectural style.
• SOAP permits XML data format only but REST permits different data format such as Plain text, HTML, XML, JSON, etc
• SOAP requires more bandwidth and resource than REST so avoid to use SOAP where bandwidth is minimal.

preg_replace('/\s/', '', 'Best Interview Question');

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PHP developers use the is_array() function to determine whether a variable is an array or not. It is available for only PHP 4 and above versions.

With the help of in_array() function we can check any element is exists in array or not. It's return type is true when element is exists and false when an element is not exists in array.

Syntax

in_array(search,array,type)

The ionCube Loader is an advanced component used by developers on the server to run encoded files. It protects the source code. When our PHP code gets pre-compiled and encrypted and requires a separate PHP module to load it, ionCube PHP loader will be required at that scenario.

In PHP, both setters and getters are methods used by developers to obtain or declare variables, especially the private ones.

Why are they important?

They are crucial because these methods allow for a certain location which will be able to handle before declaring it or while reverting it back to the developers.

There are two ways to increase the maximum execution time of a script in PHP available as following.

Method 1: Update php.ini file

To complete this process, we have to open the php.ini file and rearrange the max_execution_time (in seconds) as per our desired time.

Syntax

max_execution_time = 180 //180 seconds = 3 minutes

Method 2: Update .htaccess file

php_value max_execution_time 300

Method 3: Update your .php file

Here, we have to place the below-mentioned syntax on top of the PHP script.

ini_set('max_execution_time', 300);
ini_set('max_execution_time', 0);

In PHP, developers use the break statement to terminate a block and gain control out of the loop or switch, whereas the continue statement will not terminate the loop but promotes the loop to go to the next iteration. The break statement can be implemented in both loop (for, while do) and switch statement, but the continue statement can be only implemented in the loop (for, while do) statements.

The php.ini file is a default configuration file present in applications that require PHP. Developers use it to control different variables such as file timeouts, resource limits and upload sizes.

Here are the different types of print functions available in PHP for developers use:

• Print() Function
• Printf() Function
• Echo() Function
• Sprintf() Function
• Print_r() Function
• Var_dump() Function

First, create a sendEmail.php file in web document root and we have to use the below-mentioned script in it to send email using a PHP script. Change the $to_email with a recipient email address, $body and $subject as you require, and $from_email with a sender email address here.

We have to use the bellow mentioned syntax to swap two number using PHP, with or without using the third variable.

Here is the program we can use to get LCM of two number using PHP.

We can use document.formname.submit()

In PHP, a friend function is one non-member function having access to private and protected members within a class. A friend function has the best use case when being shared among multiple classes, which can be declared either as member functions within a class or even a global function.

In PHP, the urlencode() function is one that can be conveniently used to encode any string before actually using it as part of the URL in a query. This function is a very efficient way to pass variables onto the next page. Whereas, the urldecode() function is used to decode the above-encoded string into a readable format.

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The default session time in PHP is 1440 seconds or 24 minutes. The default session path is a temporary folder/tmp.

In PHP, Design patterns are technically a description of communication between objects and classes which are customized in order to solve a common obstacle related to designs in a particular context. Basically, they provide a common reusable solution to everyday programming problems. Design patterns or templates help in speeding up the process of web development and can be used multiple times in different scenarios as required.

Cross-Site Scripting (XSS) is one of the most common and dangerous security vulnerabilities existing within web applications. It is a means to gain unauthorized access by attacking PHP scripts present in your web app.

In PHP, an abstract class is one in which there is at least one abstract method. An abstract method is one that is declared as a method but not implemented in the code as the same.

In PHP, the “This” keyword is a reference to a PHP object which has been created by the interpreter for the user containing an array of variables. If “this” keyword is called inside a normal method within a normal class, it returns the object to the appropriate method.

Exception handling was introduced in PHP 5 as a new way for the execution of code and what exceptions to make in code in case of a specific error.

There are various keywords of exception handling in PHP like:

Try: This try block consists of the code which could potentially throw an exception. All the code in this try block is executed unless and until an exception is thrown.

Throw: This throw keyword is used to alert the user of a PHP exception occurrence. The runtime will then use the catch statement to handle the exception.

Catch: This keyword is called only when there is an exception in the try block. The code of catch must be such that the exception thrown is handled efficiently.

Finally: This keyword is used in PHP versions 5.5 and above where the code runs only after the try and catch blocks have been executed. The final keyword is useful for situations where a database needs to be closed regardless of the occurrence of an exception and whether it was handled or not.

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