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PHP Interview Questions


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

It is used to print a data in the webpage, Example:

<?php echo 'Welcome you in compuhelp'; ?> 

The above code print the text in the webpage

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

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.

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.

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 .

Eg : var $arr = array('apple', 'grape', 'lemon');

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

Example:Example print('PHP Interview questions');

print 'welcome you in compuhelp ');

in_array used to checks if a value exists in an array

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

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

Setcookie("Compuhelp", "sunil guleria", time()+3600);

eg : echo $_COOKIE["user"];

Create session : session_start();

Set value into session : $_SESSION['USER_ID']=1;

Remove data from a session : unset($_SESSION['USER_ID'];

for,while,do while and foreach

mysql_connect(servername,username,password);

mysql_select_db($db_name);

$my_qry = mysql_query("SELECT * FROM `users` WHERE `u_id`='1'; ");

$result = mysql_fetch_array($my_qry);

echo $result['First_name'];

1. mysql_fetch_row

2. mysql_fetch_array

3. mysql_fetch_object

4. mysql_fetch_assoc

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.

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

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

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

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

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.

The following code can be used:-

header("Location:index.php");

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

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

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

It is used to generate random numbers.If called without the arguments it returns a pseudo-random integer between 0 and getrandmax(). If you want a random number between 6 and 12 (inclusive), for example, use rand(6, 12).This function does not generate cryptographically safe values, and should not be used for cryptographic uses. If you want a cryptographically secure value, consider using openssl_random_pseudo_bytes() instead.

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

mysql_fetch_assoc() function Fetch a result row as an associative array, While mysql_fetch_array() fetches an associative array, a numeric array, or both

Associative arrays are arrays that use string keys is called associative arrays.

"method" attribute determines how to send the form-data into the server.There are two methods, get and post. The default method is get.This sends the form information by appending it on the URL.Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

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

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.

We can create input fields with same name for "name" attribute with squire bracket at the end of the name of the name attribute, It passes data as an array to PHP.

<input name="MyArray[]" />  <input name="MyArray[]" />  <input name="MyArray[]" /> <input name="MyArray[]" />

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

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);

The date() function provides you with a means of retrieving the current date and time, applying the format integer parameters indicated in your script to the timestamp provided or the current local time if no timestamp is given. In simplified terms, passing a time parameter is optional - if you don't, the current timestamp will be used.

There is a good page in the php manual on the subject, in short mysql_pconnect() makes a persistent connection to the database which means a SQL link that do not close when the execution of your script ends. mysql_connect()provides only for the databasenewconnection while using mysql_pconnect , the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection... the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use.

It is used for sort an array by key in reverse order.

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.

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

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

Here are three basic types of runtime errors in PHP:

2. Warnings: These are more serious errors - for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.

3. Fatal errors: These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP's default behavior is to display them to the user when they take place.

Read/Write. Creates a new file. Returns FALSE and an error if file already exists.

strpos() is used to find the position of the first occurrence of a substring in a string?

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.