PHP Interview Questions

 The two most common ways to start and finish a PHP script are:

<?php [ — PHP code—- ] ?> and <? [— PHP code —] ?>

PHP can be considered as a partial case-sensitive language. The variable names are completely case-sensitive but function names are not. Also, user-defined functions are not case-sensitive but the rest of the language is case-sensitive.

For example, user-defined functions in PHP can be defined in lowercase but later referred to in uppercase, and it would still function normally.

The three basic classes of errors are notices (non-critical), warnings (serious errors) and fatal errors (critical errors).

It is possible to use the document.form.submit() function to submit the form. For example: <input type=button value=”SUBMIT” onClick=”document.form.submit()”>

In PHP, @ is used for suppressing error messages. If any runtime error occurs on the line which consists @ symbol at the beginning, then the error will be handled by PHP.

A PHP parser is software that converts source code into the code that computer can understand. This means whatever set of instructions we give in the form of PHP code is converted into a machine-readable format by the parser.

You can parse PHP code with PHP using the token_get_all() function.

The old name of PHP was Personal Home Page.

The strip slashes function enables us to remove the escape characters before apostrophes in a string.

• Laravel
• CodeIgniter
• Symfony
• CakePHP
• Yii
• Zend Framework
• Phalcon
• FuelPHP
• PHPixie
• Slim

The header() function is used to send a raw HTTP header to a client. It must be called before sending the actual output. For example, you can't print any HTML element before using this function.

 PEAR means “PHP Extension and Application Repository”. It extends PHP and provides a higher level of programming for web developers.

There are two main rules that you have to follow when naming a variable in PHP. They are as follows:

• Variables can only begin with letters or underscores.
• Special characters such as +, %, -, &, etc. cannot be used.

NULL is a special data type in PHP used to denote the presence of only one value, NULL. You cannot assign any other value to it.

NULL is not case sensitive in PHP and can be declared in two ways as shown below:

$var = NULL:

Or

$var = null;

Both of the above syntaxes work fine in PHP.

Constants can be defined easily in PHP by making use of the define() function. This function is used to define and pull out the values of the constants easily.

Constants, as the name suggests, cannot be changed after definition. They do not require the PHP syntax of starting with the conventional $ sign.

The constant() function is used to retrieve the values predefined in a constant variable. It is used especially when you do not know the name of the variable.

 $GLOBALS is an associative array including references to all variables which are currently defined in the global scope of the script.

  Sessions automatically end when the PHP script finishes executing but can be manually ended using the session_write_close().

The PHP code always starts with <?php and ends with ?>. The block of PHP code are:

<?php   [ --Content of PHP code-- ]   ?>

Comments are used to prevent the execution of the statement. It is ignored by the compiler. In PHP, there are two types of comments: single-line comments and multi-line comments

• Single-line comment: The comment is started with double forward-slash (//).
• Multi-line comment: The comments are enclosed within /* comment section */

The count() function in PHP is used to count the number of elements present in the array. The function might return 0 for the variable that has been set to an empty array. Also for the variable which is not set the function returns 0.

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

When the value of a variable is used as the name of the other variables then it is called variable variables. $$ is used to declare variable variables in PHP.

Sample code:

$str = "PHP";
$$str = " Programming"; //declaring variable variables
echo "$str ${$str}"; //It will print "PHP programming"
echo "$PHP"; //It will print "Programming"

PHP has some unique features, which include:

• Open-source
• Platform Independent
• Case sensitive
• Flexibility
• Efficiency
• Third-party application support and security
• Interpreted

To use the image function, we will need the GD library.

Following are some popular Content Management Systems (CMS):

• WordPress
• Shopify
• Drupal
• Joomla
• Wix
• Magento

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.

 In PHP, the “$message” has a fixed name and value. It’s a regular PHP variable. On the other hand, the “$$message” is a reference variable. It holds data about the variable in question. The value in the “$$message” changes when the value in the main variable changes.

To be able to pass a variable by reference, we use an ampersand in front of it, as follows $var1 = &$var2

The differences between indexed and associative arrays in PHP are as follows:

• Indexed arrays have their keys or indexes. However, each key in an associative array has its value.
• PHP automatically assigns value to indexes in an indexed array. An index of an array starts from “0”. Associative arrays need the manual assignment of keys, and these keys can hold even strings.

PHP is case-sensitive but not fully. Variable names in PHP are case-sensitive. However, PHP function names aren’t case-sensitive. Programmers can define a function name using lowercase, and they can call these functions using uppercase. The other aspects of PHP are case-sensitive.

We have to enable the Magic quotes entry in the configuration file of PHP.

PHP developers use constructs like “include” and “require” to include files. The “require_once” expression has some similarities with “require”. However, this expression checks whether the specified file is already included. It doesn’t include the file if that’s already included.

Version 7.1 or 7.2 is the recommended version of PHP.

The browser obtains raw HTTP headers from the PHP header() function which is used to redirect it to some other location. After calling the header() function, the exit() function is used to prevent the rest of the code from getting parsed.

In case of a problem in loading a file, the require () causes a fatal error stops the script's execution. In case of the same problem, the include() issues a warning but the execution of the script continues.

The final keyword prefixes the definition of a method with itself and prevents the method from being overriden by a child class. If a class is defined as final, it means that the class cannot be extended.

The boolean function isset determines if a variable is set and is not NULL.

Two methods are possible: 

<!--?php echo "Method 1"; print "Method 2"; ?-->

We use the operator '==' to test is two objects are instanced from the same class and have same attributes and equal values. We can test if two objects are referring to the same instance of the same class by the use of the identity operator '==='.

The strip_tags() function enables us to clean a string from the HTML tags.

The use of the function session_start() lets us activating a session.

"13" and 12 can be compared in PHP since it casts everything to the integer type.

The define() directive lets us defining a constant as follows:

define ("ACONSTANT", 123);

The PHP-OpenSSL extension provides several cryptographic operations including generation and verification of digital signatures.

To be able to connect to a MySQL database, we must use mysqli_connect() function as follows:

<!--?php $database = mysqli_connect("HOST", "USER_NAME", "PASSWORD");
mysqli_select_db($database,"DATABASE_NAME"); ?-->

The result set can be handled using mysqli_fetch_array, mysqli_fetch_assoc, mysqli_fetch_object or mysqli_fetch_row.

Yes, it's possible to integrate (Distributed) Component Object Model components ((D)COM) in PHP scripts which is provided as a framework.

PHP means PHP: Hypertext Processor.

The default session time in php is until the closing of the browser

PHP syntax resembles Perl and C.