Friday, 13 March 2009

PHP Interview Questions And Answers Set - 1

What is PHP?
Answer: PHP stands for “PHP Hypertext Preprocessor”. PHP is a programming language that allows web developers to create dynamic content that interacts with databases. PHP is basically used for developing web based applications.

How can we know the number of days between two given dates using PHP?
Answer: Simple arithmetic:
$datevar1 = date('Y-m-d');
$datevar2 = '2005-07-01';
$daysvar = (strtotime() - strtotime()) / (60 * 60 * 24);
echo "Number of days since '2005-07-01': $daysvar";

What is meant by PEAR in php?
Answer: PEAR stands for “PHP Extension and Application Repository”. PEAR is the next revolution in PHP. This repository is bringing higher level programming to PHP. PEAR is a framework and distribution system for reusable PHP component. It eases installation by bringing an automated wizard, and packing the strength and experience of PHP users into a nicely organised OOPs library. PEAR also provides a command-line interface that can be used to automatically install "packages"

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

Anwser :$var is a simple variable whereas $$var is a reference variable. Example:
$user = 'ashwani'

is equivalent to

$holder = 'kumar';
$$holder = 'ashwani';


What Is a Persistent Cookie?
Answer: A persistent cookie is a cookie which is stored in a cookie file permanently on the browser's computer. By default, cookies are created as temporary cookies which stored only in the browser's memory. When the browser is closed, temporary cookies will be erased. You should decide when to use temporary cookies and when to use persistent cookies based on their differences:
*Temporary cookies can not be used for tracking long-term information.
*Persistent cookies can be used for tracking long-term information.
*Temporary cookies are safer because no programs other than the browser can access them.
*Persistent cookies are less secure because users can open cookie files see the cookie values.
What does a special set of tags do in PHP?
The output is displayed directly to the browser.
How do you define a constant?
Via define() directive, like define ("MYCONSTANT", 100);

What Is a Session?
Answer: A session is a logical object created by the PHP engine to allow you to preserve data across subsequent HTTP requests.

There is only one session object available to your PHP scripts at any time. Data saved to the session by a script can be retrieved by the same script or another script when requested from the same visitor.

Sessions are commonly used to store temporary data to allow multiple PHP pages to offer a complete functional transaction for the same visitor.

What are the differences between require and include, include_once?
Anwser : require_once() and include_once() are both the functions to include and evaluate the specified file only once. If the specified file is included previous to the present call occurrence, it will not be done again.

But require() and include() will do it as many times they are asked to do.

Anwser : The include_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include() statement, with the only difference being that if the code from a file has already been included, it will not be included again. The major difference between include() and require() is that in failure include() produces a warning message whereas require() produces a fatal errors.

Anwser : All three are used to an include file into the current page.
If the file is not present, require(), calls a fatal error, while in include() does not.
The include_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include() statement, with the only difference being that if the code from a file has already been included, it will not be included again. It des not call a fatal error if file not exists. require_once() does the same as include_once(), but it calls a fatal error if file not exists.

Anwser : File will not be included more than once. If we want to include a file once only and further calling of the file will be ignored then we have to use the PHP function include_once(). This will prevent problems with function redefinitions, variable value reassignments, etc.

What is the difference b/w mysql_fetch_object and mysql_fetch_array?
Answer: MySQL fetch object will collect first single matching record where mysql_fetch_array will collect all matching records from the table in an array

How can W execute a PHP script using command line?

Answer: Just run the PHP CLI (Command Line Interface) program and provide the PHP script file name as the command line argument. For example, "php myScript.php", assuming "php" is the command to invoke the CLI program.
Be aware that if your PHP script was written for the Web CGI interface, it may not execute properly in command line environment.

We are trying to assign a variable the value of 0123, but it keeps coming up with a different number, what?s the problem?
Answer: PHP Interpreter treats numbers beginning with 0 as octal.

Would We use print "$b dollars" or "{$b} dollars" to print out the amount of dollars in this example?
Answer: In this example it would not matter, since the variable is all by itself, but if you were to print something like "{$b},000,000 mln dollars", then you definitely need to use the braces.

What are the different tables present in MySQL? Which type of table is generated when we are creating a table in the following syntax: create table employee(eno int(2),ename varchar(10))?

Answer: Total 5 types of tables we can create
1. MyISAM
2. Heap
3. Merge
4. INNO DB
5. ISAM
MyISAM is the default storage engine as of MySQL 3.23. When you fire the above create query MySQL will create a MyISAM table.

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