PHP Interview Questions

What is PHP?
PHP: Hypertext Preprocessor 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.

What is the use of "echo" in PHP?
It is used to print a data in the web page,
Example: <?php echo 'Hello'; ?> ,
the following code print the text in the web page

How to include a file to a php page?

We can include a file using "include() " or "require()" function with file path as itsparameter.

What's the difference between include and require?

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.

Differences between GET and POST methods ?

We can send 1024 bytes using GET method but POST method can transfer large amount of data and POST is the secure method than GET method .

Require_once(), require(), include().What is difference between them?

Require() includes and evaluates a specific file, while require_once() does that only if it has not been included before (on the same page). So, require_once() is recommended to use when you want to include a file where you have a lot of functions for example. This way you make sure you don't include the file more times and you will not get the "function re-declared" error.

How to declare an array in php?

Eg : var $arr = array('Abc', 'bca', 'cab');

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.
Example print('PHP Interview questions');
print 'Job Interview ');

What is use of in_array() function in PHP ?

in_array used to checks if a value exists in an array

What is use of count() function in php ?

count() is used to count all elements in an array, or something in an object

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 fatalerror 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?

The main difference between sessions and cookies is that sessions are stored on the server, and cookies are stored on the user’s computers in the text file format. Cookies can not hold multiple variables,But Session can hold multiple variables.We can set expiry for a cookie,The session only remains active as long as the browser is open.Users do not have access to the data you stored in Session,Since it is stored in the server.Session is mainly used for login/logout purpose while cookies using for user activity tracking.

Distinguish between urlencode and urldecode?

This method is best when encode a string to used in a query part of a url. it returns a string in which all non-alphanumeric characters except -_. have replece with a percentege(%) sign . the urldecode->Decodes url to encode string as any %and other symbole are decode by the use of the urldecode() function.

What are the different errors in PHP?

In PHP, there are three types of runtime errors, they are:

Warnings:
These are important errors. Example: When we try to include () file which is not available. These errors are showed to the user by default but they will not result in ending the script.
Notices:
These errors are non-critical and trivial errors that come across while executing the script in PHP. Example: trying to gain access the variable which is not defined. These errors are not showed to the users by default even if the default behavior is changed.
Fatal errors:
These are critical errors. Example: instantiating an object of a class which does not exist or a non-existent function is called. These errors results in termination of the script immediately and default behavior of PHP is shown to them when they take place. Twelve different error types are used to represent these variations internally.

what is sql injection ?

SQL injection is a malicious code injection technique.It exploiting SQL vulnerabilities in Web applications.

How to delete a file from the system

Unlink() deletes the given file from the file system.

How to get the value of current session id?

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

What are the differences between mysql_fetch_array(), mysql_fetch_object(), mysql_fetch_row()?

Mysql_fetch_array Fetch a result row as an associative array, a numeric array, or both.

mysql_fetch_object ( resource result ) Returns an object with properties that correspond to the fetched row and moves the internal data pointer ahead. Returns an object with properties that correspond to the fetched row, or FALSE if there are no more rows

mysql_fetch_row() fetches one row of data from the result associated with the specified result identifier. The row is returned as an array. Each result column is stored in an array offset, starting at offset 0.

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

They are both variables. But $var is a variable with a fixed name. $$var is a variable who's name is stored in $var. For example, if $var contains "message", $$var is the same as $message.

What are the encryption techniques in PHP

MD5 PHP implements the MD5 hash algorithm using the md5 function,
eg : $encrypted_text = md5 ($msg);

mcrypt_encrypt :- string mcrypt_encrypt ( string $cipher , string $key , string $data , string $mode [, string $iv ] );
Encrypts plaintext with given parameters

What is the use of the function html entities?

htmlentities Convert all applicable characters to HTML entities This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.

What is the use of "enctype" attribute in a html form?

The enctype attribute determines how the form-data should be encoded when submitting it to the server. We need to set enctype as "multipart/form-data"when we are using a form for uploading files.

How to set cookies in PHP?

Setcookie("sample", "ram", time()+3600);

How to Retrieve a Cookie Value?

eg : echo $_COOKIE["user"];

How to create a session? How to set a value in session ? How to Remove data from a session?

Create session : session_start();
Set value into session : $_SESSION['USER_ID']=1;
Remove data from a session : unset($_SESSION['USER_ID'];

what types of loops exist in php?

for,while,do while and foreach

How to create a mysql connection?

mysql_connect(servername,username,password);

How to select a database?

mysql_select_db($db_name);

How to execute an sql query? How to fetch its result ?

$my_qry = mysql_query("SELECT * FROM `users` WHERE `u_id`='1'; ");
$result = mysql_fetch_array($my_qry);
echo $result['First_name'];

How we can retrieve the data in the result set of MySQL using PHP?

1. mysql_fetch_row

2. mysql_fetch_array

3. mysql_fetch_object

4. mysql_fetch_assoc

What is the use of explode() function ?

Syntax : array explode ( string $delimiter , string $string [, int $limit ] );
This function breaks a string into an array. Each of the array elements is a substring of string formed by splitting it on boundaries formed by the string delimiter.

What is the difference between explode() and split() functions?

Split function splits string into array by regular expression. Explode splits a string into array by string.

What is the use of mysql_real_escape_string() function?

It is used to escapes special characters in a string for use in an SQL statement

Write down the code for save an uploaded file in php.

if ($_FILES["file"]["error"] == 0)
{
move_uploaded_file($_FILES["file"]["tmp_name"],
      "upload/" . $_FILES["file"]["name"]);
      echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
}

How to create a text file in php?

$filename = "/home/user/guest/newfile.txt";
$file = fopen( $filename, "w" );
if( $file == false )
{
echo ( "Error in opening new file" ); exit();
}
fwrite( $file, "This is a simple test\n" );
fclose( $file );

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 used for it, header("Location:index.php");

How stop the execution of a php scrip ?

exit() function is used to stop the execution of a page

How to set a page as a home page in a php based site ?

index.php is the default name of the home page in php based sites

How to find the length of a string?

strlen() function used to find the length of a string

What is the importance of "action" attribute in a html form?

The action attribute determines where to send the form-data in the form submission.

How do you define a constant?

Using define() directive, like define ("MYCONSTANT",150)

How send email using php?

To send email using PHP, you use the mail() function.This mail() function accepts 5 parameters as follows (the last 2 are optional). You need webserver, you can't send email from localhost. eg : mail($to,$subject,$message,$headers);