PHP Interview Questions and Answers Programming

Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you. It is a dependency manager

• It enables you to declare the libraries you depend on.
• Finds out which versions of which packages can and need to be installed, and installs them (meaning it downloads them into your project).
  • composer init - to launch a wizard
  • composer require - to add a dependency, also creates a composer.json to manage dependencies
  • composer.lock - this file ensures that everyone in the project uses the same version of the packages by not allowing newer versions to be downloaded

This is one of the most frequently asked PHP interview questions and answers for freshers in recent times. 

PSR Stands for PHP Standard Recommendations. These are some guidelines created by the community to bring a standard to projects/Libraries and have a common language which everyone can speak and understand.

• Basic coding standard
• Coding style. Guide
• Logger interface
• Autoloading standard
• Caching interface
• HTTP Message interface
• Container interface
• Hypermedia links
• Http Handlers
• Simple cache
• HTTP Factories
• HTTP CLIENT

Here are some steps you can follow to check the syntax of PHP. Ensure PHP CLI is installed on your machine. Browse to the relevant folder where the code is. Run the command php -l testfile.phpvia command line.

This will detect any syntax errors in the code and display on a terminal

Expect to come across this, one of the most important PHP interview questions for experienced professionals in programming, in your next interviews. 

PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with some additional features useful for sites of any size, especially busier sites. These features include:

• Adaptive process spawning (NEW!)
• Basic statistics (ala Apache's mod_status) (NEW!)
• Advanced process management with graceful stop/start
• Ability to start workers with different uid/gid/chroot/environment and different php.ini (replaces safe_mode)
• Stdout & stderr logging
• Emergency restart in case of accidental opcode cache destruction
• Accelerated upload support
• Support for a "slowlog"
• Enhancements to FastCGI, such as fastcgi_finish_request() - a special function to finish request & flush all data while continuing to do something time-consuming (video converting, stats processing, etc.)

A must-know for anyone looking for top core PHP interview questions, this is one of the most frequently asked PHP interview questions. 

Xdebug is an extension for PHPto assist with debugging and development. It contains a single step debuggerto use with IDEs; it upgrades PHP's var_dump() function; it adds stack tracesfor Notices, Warnings, Errors and Exceptions; it features functionality for recording every function call and variable assignmentto disk; it contains a profiler; and it provides code coveragefunctionality for use with PHPUnit.

Xhprof: Xhprof was created by Facebook and includes a basic UI for reviewing PHP profiler data. It aims to have a minimum impact on execution times and requires relatively little space to store a trace. Thus, you can run it live without a noticeable impact on users and without exhausting the memory.

In order to reduce RTT ( Round trip time ), websockets becomes handy if you are thinking about performance.

1. WebSocket is a protocol for creating a fast two-way channel between a web browserand a server. WebSocket overcomes limitations with HTTP to allow for low latency communications between a user and a web service
2. PHP supports WebSockets and the following projects help us use them in our projects:
   
   i.   https://socketo.me 

Web Servers themselves cannot understand and parse PHP files, the external programs do it for them. There are many ways how you can do this, both with its pros and cons. Various ways:

1. Mod_php: means PHP, as an Apache module
2. FastCGI: a PHP process is launched by Apache, and it is that PHP process that interprets PHP code -- not Apache itself
3. PHP-FPM: PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with some additional features useful for sites of any size, especially busier sites

Here are the use-cases for array_map, array_reduce and array_walk.

1. Array_map: Applies the callback to the elements of the given arrays
2. Array_reduce: Iteratively reduce the array to a single value using a callback function
3. Array_walk: Apply a user supplied function to every member of an array

<?php
$originalarray1 = array(2.4, 2.6, 3.5);
$originalarray2 = array(2.4, 2.6, 3.5);
print_r(array_map('floor', $originalarray1)); // $originalarray1 stays the same
// changes $originalarray2
array_walk($originalarray2, function (&$v, $k) { $v = floor($v); }); print_r($originalarray2);
// this is a more proper use of array_walk
array_walk($originalarray1, function ($v, $k) { echo "$k => $v", "\n"; });
//  array_map accepts several arrays print_r(
array_map(function ($a, $b) { return $a * $b; }, $originalarray1, $originalarray2)
);
//  select only elements that are > 2.5
print_r(
array_filter($originalarray1, function ($a) { return $a > 2.5; })
);
?>
Array
(
[0]  => 2
[1]  => 2
[2]  => 3
)
Array
(
[0]  => 2
[1]  => 2
[2]  => 3
)
0 => 2.4
1 => 2.6
2 => 3.5
Array
(
[0]  => 4.8
[1]  => 5.2
[2]  => 10.5
)
Array
(
[1]  => 2.6
[2]  => 3.5
)

An inherited member from a base class is overridden by a member inserted by a Trait. The precedence order is that members from the current class override Trait methods, which in turn override inherited methods. An inherited method from a base class is overridden by the method inserted into MyHelloWorld from the SayWorld Trait.

The behaviour is the same for the methods defined in the MyHelloWorld class. The precedence order is that methods from the current class override Trait methods, which in turn override methods from the base class.

trait A {
function calc($v) {
return $v+1;
}
}
class MyClass {
use A {
calc as protected traitcalc;
}
function calc($v) {
$v++;
return $this->traitcalc($v);
}
}

This is one of the most frequently asked PHP interview questions for freshers in recent times.

Performance is a very important aspect considered in any language at runtime. In order to improve the performance of the PHP runtime engine, OPcache can help in a significant way.

1. OPcache improves PHP performance by storing precompiled script bytecode in shared memory, thereby removing the need for PHP to load and parse scripts on each request.
2. OPcache is bundled with PHP 5.5 and higher. OPcache is more closely bound to PHP itself than other bytecode cache engines like APC.
3. The whole cache engine works in the background and is transparent to a visitor or a web developer. In order to check its status, you may use one of the two functions that provide such information: opcache_get_configuration() and opcache_get_status()

• Event Loop is a concept from Javascript. In a single threaded execution, the code is waiting for the activity to get over before moving ahead. Event Loop helps us utilize the waiting period to execute code.
• PHP supports Event loop. There are multiple libraries which help us use event loop in our project
  • https://github.com/reactphp
  • https://github.com/icicleio
  • https://github.com/asyncphp/doorman

Don't be surprised if this question pops up as one of the top advanced PHP interview questions in your next attempt. 

A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions. The following is a list of functions which create, use or destroy PHP resources. The function is_resource() can be used to determine if a variable is a resource and get_resource_type() will return the type of resource it is. https://www.php.net/manual/en/resource.php

This is a common yet one of the most important PHP coding interview questions and answers for experienced professionals, don't miss this one.

Generators provide an easy way to implement simple iterators without the overhead or complexity of implementing a class that implements the Iterator interface. A generator allows you to write code that uses foreach to iterate over a set of data without needing to build an array in memory, which may cause you to exceed a memory limit, or require a considerable amount of processing time to generate. Instead, you can write a generator function, which is the same as a normal function, except that instead of returning once, a generator can yield as many times as it needs to in order to provide the values to be iterated over.

<?php
function nums() {
echo "The generator has startedn";
for ($i = 0; $i < 5; ++$i) {
yield $i;
echo "Yielded $in";
}
echo "The generator has endedn";
}
foreach (nums() as $v);

One of the most frequently posed PHP basic interview questions, be ready for this conceptual question.

Promises becomes very important when it comes to asynchronous communication and it also provides effective ways to manage resources.

1. A promise is an object that may produce a single value sometime time in the future: either a resolved value, or a reason that it’s not resolved (e.g., a network error occurred). A promise may be in one of 3 possible states: fulfilled, rejected, or pending. Promise users can attach callbacks to handle the fulfilled value or the reason for rejection.
2. It started with JS but has been implemented in variety of technologies including PHP.
3. Some libraries we can use to implement promises in PHP:
4. https://github.com/guzzle/promises
5. https://github.com/reactphp/promise

Here is the code snippet for reference.

<?php
$array = array (1, 3, 3, 8, 15); $my_val = 3;
$filtered_data = array_filter($array, function ($element) use ($my_val) { return ($element != $my_val); } ); print_r($filtered_data);
?>

A staple in PHP developer interview questions and answers, be prepared to answer this one using your hands-on experience.

1. The indexes used in an ArrayAccess object are not limited to strings and integers as they are for arrays: you can use any type for the index as long as you write your implementation to handle them. This fact is exploited by the SplObjectStorage class.
2. ArrayAccess Interface: Interface to provide accessing objects as arrays class obj implements ArrayAccess {

private $container = array();
public function __construct() {
$this->container = array(
"one" => 1,
"two" => 2,
"three" => 3,
);
}
public function offsetSet($offset, $value) {
if (is_null($offset)) {
$this->container[] = $value;
} else {
$this->container[$offset] = $value;
}
}
public function offsetExists($offset) {
return isset($this->container[$offset]);
}
public function offsetUnset($offset) {
unset($this->container[$offset]);
}
public function offsetGet($offset) {
return isset($this->container[$offset]) ? $this->container[$offset] : null;
}
}
$obj = new obj;
var_dump(isset($obj["two"]));
var_dump($obj["two"]);
unset($obj["two"]);
var_dump(isset($obj["two"]));
$obj["two"] = "A value";
var_dump($obj["two"]);
$obj[] = 'Append 1';
$obj[] = 'Append 2';
$obj[] = 'Append 3';
print_r($obj);
bool(true)
int(2)
bool(false)
string(7) "A value"
obj Object
(
[container:obj:private] => Array
(
[one] => 1
[three] => 3
[two] => A value
[0]  => Append 1
[1]  => Append 2
[2]  => Append 3
)
)

A staple in PHP interview questions for experienced, be prepared to answer this one using your hands-on experience. This is also one of the top PHP coding interview questions.

• JsonSerializable Interface: Objects implementing JsonSerializable can customize their JSON representation when encoded with json_encode().

class Items implements \JsonSerializable
{
private $var; private $var1; private $var2;
public function __construct()
{
// ...
}
public function jsonSerialize()
{
$vars = get_object_vars($this);
return $vars;
}
}

• __toString: The toString() method allows a class to decide how it will react when it is treated like as a string.

Sometime when we try to access session object we get the object class as __PHP_Incomplete_Class.
This happens when we try to initialize the session before loading the class definitions for the object we are trying to save into the session.

• To say it in simple, if class definitions are not defined, PHP creates incomplete objects of the class __PHP_Incomplete_Class.
• To avoid __php_incomplete_class object session error, every class definition must be included or defined before starting the session

This, along with other PHP basic interview questions for freshers, is a regular feature in PHP interviews, be ready to tackle it with the approach mentioned below.