Php Interview Questions

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Top PHP Interview Questions with Answers For Job

PMA10:27

What is PHP?

    PHP is a server side scripting language used for web development applications.
    Php is the powerful tool for making dynamic website.
    Many open source, free and commercial scripts    and   Stuff made by php

What is a data type?

A Data type is the classification of data into a category according to its attributes;
• Alphanumericcharacters are classified as strings
• Whole numbersare classified integers
• Numberswith decimal pointsare classified as floating points.
• True or falsevalues are classified as Boolean.
PHP is a loosely typed language;it does not have explicit defined data types.

What is a variable?

A variable is a name given to a memory location that stores data at runtime.
The scope of a variable determines its visibility.
A global variable is accessible to all the scripts in an
application. A local variable is only accessible to the script
that it was defined in.

How to retrieve a secure URL?
To retrieve secure URLs, the cURL extension needs access to an SSL library, such as OpenSSL.
<?php
$c = curl_init('https://secure.example.com/accountbalance.php');
curl_setopt($c, CURLOPT_RETURNTRANSFER, 1);
$page = curl_exec($c); curl_close($c);
?>

Why you should use variables?

Variables help separate data from the program algorithms. The same algorithm can be used
for different input data values. For example, suppose that you are developing a calculator
program that adds up two numbers, you can create two variables that accept the numbers
then you use the variables names in the expression that does the addition.

How to show all PHP runtime errors?

   Add error_reporting function set 1 .

What is htaccess?

   .htaccess files are configuration files of Apache Server which provide
   a way to make configuration changes on a per-directory basis.

How to redirect a user to a page?

header('Location: http://www.example.com/');
The redirect URL must include the protocol and hostname.

   What is echo in php?

    It is a keyword.
    It is used to print data on the webpage, like that <?php echo 'test'; ?> ,

    How to include a file to a php page?

    Add include a file using include() or require() function with the path.

    What's the difference between include and require?

    PHP provides two constructs to load code and HTML from another module: require and include.
    They both load a file as the PHP script runs, work in conditionals and loops, and complain if
    the file being loaded can't be found. The main difference is that attempting to require a
   nonexistent file is a fatal error, while attempting to include such a file produces a warning
    but does not stop script execution.

    If the file is not found by require(), it will gives a fatal error and stop the execution of the script.
    If the file is not found by include(), it will gives a warning , but execution will continue.

    will not get the "function re-declared" error.

    Differences between GET and POST methods ?
    A GET request encodes the form parameters in the URL, in what is called a query string:

    /path/to/chunkify.php?word=despicable&length=3
    A POST request passes the form parameters in the body of the HTTP request, leaving the URL untouched.
    POST requests are not idempotent. This means that they cannot be cached,
    and the server is recontacted every time the page is displayed.

    How to declare an array php?

    Example : var $arr = array('ie', 'firefox', 'safari');

    What is the use of 'print' in php?

    This is not actually a real function, It is a language construct.
    So you can use with out parentheses with its argument list.


    What is in_array() function?

    The in_array( ) function returns true or false, depending on whether the first
     argument is an element in the array given as the second argument.
    in_array used to checks if a value exists in an array that Searching for Values of array.

    What is count() function in php ?

    The count( ) and sizeof( ) functions are identical in use and effect.
    They return the number of elements in the array.

    What’s the difference between include and require?

    It’s how they handle failures. 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.

    What is the difference between Session and Cookie?

    sessions are stored on the server, and cookies are stored on the client’s computers in the text file format.
    A cookie is a bit of information that the server can give to a client.
    Every session has a data store associated with it. You can register variables to be loaded
    from the data store when each page starts and saved back to the data store when the page ends.


   How to set cookies in PHP?

    Setcookie("test", "sem", time()+3600);


    How to Retrieve a Cookie Value?
     echo $_COOKIE["test"];


    How to create a session?

    Create session by session_start();

   How to set a value in session ?

    Set value into session by $_SESSION['test_ID']=1987654;

   How to Remove data from a session?

   Remove data from session -> session_unset($_SESSION['test_ID'];

    How to create a mysql connection?
    call mysql_connect(servername,username,password);

    How to select a database?

    call mysql_select_db($db_name);

    How to execute an sql query? How to fetch its result ?
    $my_qry = mysql_query("SELECT * FROM `test` WHERE `test_id`='16'; ");
    $result = mysql_fetch_array($my_qry);
    echo $result['First_test_name'];

    How to get the resultset of MySQL using PHP?
        1. mysql_fetch_row
        2. mysql_fetch_array
        3. mysql_fetch_object
        4. mysql_fetch_assoc



    How to strip whitespace or other characters from the beginning and end of a string ?

    The trim() function removes whitespaces or other predefined characters from both sides of a string.

    What is the use of header() function in php ?

    The header() function sends a raw HTTP header to a client browser.
    Remember that this function must be called before sending the actual out put.
    For example, You do not print any HTML element before using this function.

    How to redirect a page in php?

    The following code can be add for it, header("Location:test.php");

    How stop the execution of a php scrip ?

    exit() function stop the execution of a page.


    How to get the length of a string?

    strlen() function gives the length of a string

    How to generate random numbers in php?

    Add rand function to generate random numbers.

    How to varify a variable in php?

    This is_set function is used to determine if a variable is set and is not .


    What is mean by an associative array?

    Associative arrays are arrays that indexed by string keys is called associative arrays.



    How do you define a constant?

    Using define() directive, like that define ("MYCONSTANT",765754);


    How send email using php?

    To send email using PHP, you use the mail() function.This mail() function accepts 5 parameters

    How to find current date and time?

    The date() function gives the current date and time .


    What is the use of ksort in php?

    Its sort an array by key in reverse order.

Who is the father of PHP ?

Rasmus Lerdorf is known as the father of PHP.

    How to delete a file from the system?

    Unlink() deletes the file from the file system.

    How to get the value of current session id?

    session_id() function gives the session id for the current session.

What is the difference between $name and $$name?

$name is variable where as $$name is reference variable
like $name=sonia and $$name=singh so $sonia value is singh.

mysql_fetch_object vs mysql_fetch_array?

mysql_fetch_object() is similar tomysql_fetch_array(), with one difference - an object is returned, instead of an array. Indirectly, that means that you can only access the data by the field names, and not by their offsets numbers are illegal property names

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 Â» 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.

How to Connecting two Strings?
a useful concept—concatenation. It refers to the process of linking
items together. Specifically in programming, you concatenate strings.
The period . is the operator for performing this action, and it's used like so:

$tString = $String1 . $bString2;

echo $tString;

Why we use strstr?
strstr returns all of string after the first occurrence of substring .
If substring doesn't exist in string , the function returns FALSE.

How to capitalize only the first character of a string?

you use ucfirst:

$txt = "welcome to the this site";
echo $ucfirst($txt);

What three components need to create a dynamic web page?

A web server, a server-side programming language, and a database.

What does Apache use to load extensions?

Modules.

What does the PHP Interpreter do?

It processes the HTML and PHP files.

What's a more secure function than md5() for encoding passwords?

The sh1() function creates a 160-bit key instead of md5()'s 128-bit string.

It also uses a superior algorithm for making it difficult to determine the

values that generate a particular encoding.

What are the advantages of using PEAR?

The PEAR functions are more compact, and they automate some of the manual

work of connecting to and selecting from the database. Because PEAR code

is used by many developers, it is less likely to have an error than to have code

that's written from scratch.

Learn Php Code

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PHP INTERFACES

PMA01:16

Class inheritanceenables you to describe a parent-child relationship
between classes. For example, you might have a base class
Shapefrom which both Squareand Circlederive. However,
you might often want to add additional “interfaces” to classes,
basically meaning additional
contracts to which
the class must adhere. This is achieved in C++ by using multiple
inheritance and deriving from two classes. PHP chose interfaces
as an alternative to multiple inheritance, which allows you to specify
additional contracts a class must follow. An interface is declared
similar to a class but only includes function prototypes without
implementation and constants. Any class that “implements”
this interface automatically has the interface’s constants defined and,
as the implementing class, needs to supply the function definitions for the
interface’s function prototypes that are all abstractmethods unless you
declare the implementing class as abstract.

abstract class Shape {
function setCenter($x, $y) {
$this->x = $x;
$this->y = $y;
}
abstract function draw();

protected $x, $y;
}
class Square extends Shape {
function draw()
{
// Here goes the code which draws the Square
...
}
}
class Circle extends Shape {
function draw()
{
// Here goes the code which draws the Circle
...
}
}
You can see that the draw()abstract method does not
contain any code.

To implement an interface, use the following syntax:
class A implements B, C, ... {
...
}

Classes that implement an interface have an instance of a relationship
with the interface; for example, if class Aimplements interface
myInterface, the following results in '$obj is-A myInterface'printing:

$obj = new A();
if ($obj instanceof myInterface) {
print '$obj is-A myInterface';
}

Static Methods-PHP

PMA00:42

PHP supports declaring methods as static.
Whatthis means is that your static methods are part of the
class and are not bound to any specific object instance and
its properties. Therefore, $this isn’t accessible in these methods,
but the class itself is by using selfto access it. Because
static methods aren’t bound to any specific object, you can
call them without creating an object instance by using the
class_name::method()syntax. You may also call them from an
object instance using $this->method(), but $thiswon’t
be defined in the called method. For clarity, you should use self::method()
instead of $this->method().

class PrettyPrinter {
static function printHelloWorld()
{
print "Hello, World";
self::printNewline();
}
static function printNewline()
{
print "\n";
}
}
PrettyPrinter::printHelloWorld();

The example prints the string "Hello, World"followed by a newline.
Although it is a useless example, you can see that printHelloWorld()can be
called on the class without creating an object instance using the class name,
and the static method itself can call another static method of the
class printNewline()using the self::notation. You may call a parent’s
static method by using the parent::notation.

Static Properties

As you know by now, classes can declare properties. Each instance of the
class,object has its own copy of these properties. However, a class can
also contain static properties. Unlike regular properties, these belong to
the class itself and not to any instance of it.

class propertiesas opposed to object or instance properties. You can also
think of static properties as global variables that sit inside a class but are
accessible from anywhere via the class.
Static properties are defined by using the static keyword:
class MyClass {
static $myStaticVariable;
static $myInitializedStaticVariable = 0;
}
To access static properties, you have to qualify the property name with
the class it sits in

MyClass::$myInitializedStaticVariable++;
print MyClass::$myInitializedStaticVariable;

configuring PHP-impact security

PMA05:30

The primary mechanism for configuring PHP is the php.inifile.
As the master file, this provides you with control over all configuration settings.
Entries generally take the format:
setting= value

Be sure to read the comments provided in the file before making changes, though.
There are a few tricks, such as include_pathusing a colon (:) as a seperator on
Unix, and a semicolon (;) on Windows.
Most Web hosts will not provide you access to your php.inifile unless you have
root access to the system (which is typically not the case if you’re using a cheap
virtual hosting service). Your next alternative is to use .htaccessfiles to configure
PHP assuming the Web server is Apache.
An .htaccessfile is a plain text file that you place in a public Web directory to
determine the behavior of Apache when it comes to serving pages from that directory; for instance, you might identify which pages you’ll allow public access to.
Note that the effect of an .htaccessfile is recursive—it applies to subdirectories
as well.

To configure PHP with .htaccessfiles, your hosting provider must have the
Apache setting AllowOverride Optionsor AllowOverride Allapplied to your
Web directory in Apache’s main httpd.confconfiguration file. Assuming that
is done, there are two Apache directives you can use to modify PHP’s configuration:
php_flag
used for settings that have boolean values (i.e. on/offor 1/0) such as
register_globals

php_value
used to specify a string value for settings, such as you might have with the
include_pathsetting
Here’s an example .htaccessfile:

# Switch off register globals
php_flag register_globals off
# Set the include path
php_value include_path ".;/home/username/pear"
The final mechanism controlling PHP’s configuration is the group of functions
ini_setand ini_alter, which let you modify configuration settings, as well as
ini_get, which allows you to check configuration settings, and ini_restore,
which resets PHP’s configuration to the default value as defined by php.iniand
any .htaccessfiles. Using ini_set, here’s an example which allows us to avoid
having to define our host, user name and password when connecting to MySQL:
ini_set('mysql.default_host', 'localhost');
ini_set('mysql.default_user', 'harryf');
ini_set('mysql.default_password', 'secret');
if (!mysql_connect()) {
echo mysql_error();
} else {
echo 'Success';
}
Be aware that PHP provides for some settings, such as error_reporting, alternative functions that perform effectively the same job as ini_set.

PHP-script-Related Variables

PMA12:26

PHP-script Related Variables

PHP automatically creates variables for all the data it receives in an HTTP request. This can include GET data, POST data, cookie data, and environment variables. The variables are either in PHP's global symbol table or in one of a number of superglobal arrays, depending on the value of the register_globals setting in your php.ini file.

In PHP 4.2.0 and after, the default setting for register_globals is off. With register_globals off, all the various variables that are usually available directly in the global symbol table are now available via individual superglobal arrays. There is a limited set of superglobals and they cannot be created from a user-level script. The superglobal array to use depends on the source of the variable. Here is the list:

$_GET: GET-method variables. These are the variables supplied directly in the URL. For example, with http://www.example.com/script.php?a=1&b=2, $_GET['a'] and $_GET['b'] are set to 1 and 2, respectively.
$_POST: POST-method variables. Form field data from regular POST-method forms.
$_COOKIE: Any cookies the browser sends end up in this array. The name of the cookie is the key and the cookie value becomes the array value.
$_REQUEST: This array contains all of these variables (i.e., GET, POST, and cookie). If a variable appears in multiple sources, the order in which they are imported into $_REQUEST is given by the setting of the variables_order php.ini directive. The default is 'GPC', which means GET-method variables are imported first, then POST-method variables (overriding any GET-method variables of the same name), and finally cookie variables (overriding the other two).
$_SERVER: These are variables set by your web server. Traditionally things like DOCUMENT_ROOT, REMOTE_ADDR, REMOTE_PORT, SERVER_NAME, SERVER_PORT, and many others. To get a full list, have a look at your phpinfo( ) output, or run a script like the following to have a look:

<?php
  foreach($_SERVER as $key=>$val) {
    echo '$_SERVER['.$key."] = $val<br>\n";
  }
?>

$_ENV: Any environment variables that were set when you started your web server are available in this array.
$_FILES: For RFC 1867-style file uploads the information for each uploaded file is available in this array. For example, for a file upload form containing:

<input name="userfile" type="file">

The $_FILES array will look something like this:

$_FILES['userfile']['name'] => photo.png
$_FILES['userfile']['type'] => image/png
$_FILES['userfile']['tmp_name'] => /tmp/phpo3kdGt
$_FILES['userfile']['error'] => 0
$_FILES['userfile']['size'] => 158918

Note that the 'error' field is new for PHP 4.2.0 and the values are: 0 no error, file was uploaded); 1 (the uploaded file exceeds the upload_max_filesize directive in php.ini; 2 the uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form; 3 the actual number of bytes uploaded was less than the specified upload file size; and 4.

However, having seen some of the possible values of HTTP_USER_AGENT in the last chapter, you can imagine that there are hundreds of slightly different values. So it's time to learn some basic pattern matching.

You'll use the preg_match() function to perform this task. This function needs two arguments: what you're looking for, and where you're looking:

preg_match("/[what you're looking for]/", "[where you're
looking]");

This function will return a value of true or false, which you can use in an if…else block to do whatever you want. The goal of the first script is to determine if a Web browser is Microsoft Internet Explorer, Netscape, or something else. This can be a little tricky, but not because of PHP.

Within the value of HTTP_USER_AGENT, Netscape always uses the string Mozilla to identify itself. Unfortunately, the value of HTTP_USER_AGENT for Microsoft Internet Explorer also uses Mozilla to show that it's compatible. Luckily, it also uses the string MSIE, so you can search for that. If the value of HTTP_USER_AGENT doesn't contain either Mozilla or MSIE, chances are very good that it's not one of those Web browsers.