Showing posts with label php-interview-questions-answers. Show all posts
Showing posts with label php-interview-questions-answers. Show all posts
Cookies Versus Sessions?
$_ENV and $_SERVER ?
PHP sets several variables for you containing information about the server, the
environment, and your visitor's request. These are stored in the superglobal
arrays $_ENV and $_SERVER, but their availability depends on
whether the script is being run through a web server or on the command line.
Name
|
Value
|
|---|---|
HTTP_REFERER
|
If the user clicked a link to get the current page, this will
contain the URL of the previous page, or it will be empty if the user entered
the URL directly.
|
HTTP_USER_AGENT
|
The name reported by the visitor's web browser.
|
PATH_INFO
|
Any data passed in the URL after the script name.
|
PHP_SELF
|
The name of the current script.
|
REQUEST_METHOD
|
Either GET or POST.
|
QUERY_STRING
|
Includes everything after the question mark in a GET request.
Not available on the command line.
|
Of those, HTTP_REFERER and HTTP_USER_AGENT are the most important, as you can use these two to
find out a lot about your visitor and then take the appropriate action. For
example:
<?php
if (isset($_SERVER['HTTP_REFERER'])) {
print "previously was {$_SERVER['HTTP_REFERER']}
<br />";
} else {
print "You didn't click any links to get here<br />";
}
?>
<a href="refer.php">Click me!</a>
If you load that page in your browser by typing the URL in by
hand, the "You didn't click any links to get here" text is shown because
HTTP_REFERER has not been set. However, if once the page is loaded you
follow the "Click me!" link, the page will reload itself; this time,
HTTP_REFERER will be set and the other message should appear. Although
it can be easily spoofed, HTTP_REFERER is generally a good way to make
sure a visitor came from a certain pagewhether you want to use that to say, "You
can't download my files because you came from another site" or "Welcome, Google
users!" is up to you.
Web server compression?
The best way to understand web server compression is to think of sending ZIP files
instead of uncompressed files from your web server to your web user. Sending less data
over the network will minimize network latency and your web users will get the file
faster.
The same thing applies to web spiders, as the major ones support HTTP 1.1. In fact,
search engines would appreciate the fact that they will need to use a lot less network
bandwidth to do the same work.
Web server compression is a technology used on the web server where you are hosting
your pages. If you have full control of the web server, you can set up this compression
to occur automatically for all websites or pages this server is hosting.
If you do not have this luxury, you can set this up in your code. To set up web server
compression in PHP, you can use the following PHP code:
<?php
ob_start("ob_gler");
?>
<HTML>
<body>
<p>This is the content of the compressed page.</p>
</body>
</HTML>
You can enable web server compression in your code in another way that is even easier
than the approach we just discussed. You can use the php.ini file that usually sits in
your root web folder. If it does not exist, you can create it. You can also place this file
in your subfolders to override the root php.ini settings.
instead of uncompressed files from your web server to your web user. Sending less data
over the network will minimize network latency and your web users will get the file
faster.
The same thing applies to web spiders, as the major ones support HTTP 1.1. In fact,
search engines would appreciate the fact that they will need to use a lot less network
bandwidth to do the same work.
Web server compression is a technology used on the web server where you are hosting
your pages. If you have full control of the web server, you can set up this compression
to occur automatically for all websites or pages this server is hosting.
If you do not have this luxury, you can set this up in your code. To set up web server
compression in PHP, you can use the following PHP code:
<?php
ob_start("ob_gler");
?>
<HTML>
<body>
<p>This is the content of the compressed page.</p>
</body>
</HTML>
You can enable web server compression in your code in another way that is even easier
than the approach we just discussed. You can use the php.ini file that usually sits in
your root web folder. If it does not exist, you can create it. You can also place this file
in your subfolders to override the root php.ini settings.
What is a cookie , explaing ?
Cookie is use to store the temporary data in browser memory, We can store data in cookies using setcookie('name','value','time');
we can use that rule for simple cookie, this value will store in the browser memory. If the browser is closed the cookie value will be deleted. Another way to store data in cookie file for long time:
persistent cookie using that way we can store data for long time in the user system.
we can use that rule for simple cookie, this value will store in the browser memory. If the browser is closed the cookie value will be deleted. Another way to store data in cookie file for long time:
persistent cookie using that way we can store data for long time in the user system.
How to prevent hijacking in PHP?
Make Error_reporting to E_ALL so that all variables will be intialized before using them.
Make practice of using htmlentities(), strip_tags(), utf8_decode() and addslashes() for filtering malicious data in php
Make practice of using mysql_escape_string() in mysql.
Make practice of using htmlentities(), strip_tags(), utf8_decode() and addslashes() for filtering malicious data in php
Make practice of using mysql_escape_string() in mysql.
What Is a Session?
It is stored at server side because PHP is server side scripting language
Session is stored on server side because how much time page will execute it doesn't depend on client it depends on server. Server decide the session of each page ..thats why session is stored on server side
Session is to store as the server side value
method $_session start('id');
and cookie is store the validation of client side
Session is stored on server side because how much time page will execute it doesn't depend on client it depends on server. Server decide the session of each page ..thats why session is stored on server side
Session is to store as the server side value
method $_session start('id');
and cookie is store the validation of client side
THE DIFFERENT TYPES OF ERRORS IN PHP?
1. Notices: These are trivial, non-critical errors that PHP
encounters while executing a script – for example, accessing a variable
that has not yet been defined
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.
Internally, these variations are represented by twelve different error types
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.
Internally, these variations are represented by twelve different error types
What’s the special meaning of __sleep and __wakeup?
__sleep returns the array of all the variables than need to be saved,
while __wakeup retrieves them.
while __wakeup retrieves them.
What is the difference between $age and $$age
They are both variables. But $age is a variable with a fixed name.
$$age is a variable who’s name is stored in $age. For example,
if $age contains “var”, $$age is the same as $var.
$test = ‘abcd';
is equivalent to
$holder = ‘test';
$$holder = ‘abcd';
$test = ‘abcd';
is equivalent to
$holder = ‘test';
$$holder = ‘abcd';
How many values can the SET function of MySQL take?
MySQL set can take zero or more values but at the maximum it can
take 64 values
take 64 values
What is the maximum size of a file that can be uploaded using PHP and how can we change this?
By default the maximum size is 2MB.
can change the size
setup at php.ini
upload_max_filesize = 12M
can change the size
setup at php.ini
upload_max_filesize = 12M
How can we encrypt the username and password using PHP?
The functions in this section perform encryption and decryption
| encryption | decryption |
| AES_ENCRYT() | AES_DECRYPT() |
| ENCODE() | DECODE() |
| DES_ENCRYPT() | DES_DECRYPT() |
| ENCRYPT() | Not available |
| MD5() | Not available |
| OLD_PASSWORD() | Not available |
| PASSWORD() | Not available |
| SHA() or SHA1() | Not available |
| Not available | UNCOMPRESSED_LENGTH() |
count the elements of an array?
sizeof($array) – This function is an alias of count()
count($urarray) – This function returns the number of elements in an array.
count($urarray) – This function returns the number of elements in an array.
What are “GET” and “POST”?
GET: we are submitting a form to login.php, when we do submit or similar
action, values are sent through visible query string (notice
./login.php?username=…&password=… as URL when executing the script
login.php) and is retrieved by login.php by $_GET['username'] and
$_GET['password'].
POST: we are submitting a form to login.php, when we do submit or similar action, values are sent through invisible standard input (notice ./login.php) and is retrieved by login.php by $_POST['username'] and $_POST['password'].
POST method data is sent by standard input (nothing shown in URL when posting while in GET method data is sent through query string.
POST: we are submitting a form to login.php, when we do submit or similar action, values are sent through invisible standard input (notice ./login.php) and is retrieved by login.php by $_POST['username'] and $_POST['password'].
POST method data is sent by standard input (nothing shown in URL when posting while in GET method data is sent through query string.
What is the default session time in php and how can I change it?
The default session time in php is until closing of browser
What are the MySQL database files stored in system ?
Data is stored in name.myd
Table structure is stored in name.frm
Index is stored in name.myi
Table structure is stored in name.frm
Index is stored in name.myi