Top 100 PHP Interview Questions & Answers
Feb 12, 2013 by admin
1) What is
PHP?
PHP is a web
language based on scripts that allows developers to dynamically create
generated web pages.
2) What does
the initials of PHP stand for?
PHP means
PHP: Hypertext Preprocessor.
3) Which
programming language does PHP resemble to?
PHP syntax
resembles Perl and C
4) What does
PEAR stands for?
PEAR means
“PHP Extension and Application Repository”. it extends PHP and provides a
higher level of programming for web developers.
5) What is
the actually used PHP version?
Version 5 is
the actually used version of PHP.
6) How do
you execute a PHP script from the command line?
Just use the
PHP command line interface (CLI) and specify the file name of the script to be
executed as follows:
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php script.php
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7) How to
run the interactive PHP shell from the command line interface?
Just use the
PHP CLI program with the option -a as follows:
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php -a
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8 What are
the correct and the most two common way to start and finish a PHP block of
code?
The two most
common ways to start and finish a PHP script are: <?php [
--- PHP code---- ] ?> and <? [--- PHP code ---] ?>
9) How can
we display the output directly to the browser?
To be able
to display the output directly to the browser, we have to use the special tags
<?= and ?>.
10) What is
the main difference between PHP 4 and PHP 5?
PHP 5
presents many additional OOP (Object Oriented Programming) features.
11) Is
multiple inheritance supported in PHP?
PHP includes
only single inheritance, it means that a class can be extended from only one
single class using the keyword ‘extended’.
12) What is
the meaning of a final class and a final method?
‘final’ is
introduced in PHP5. Final class means that this class cannot be extended and a
final method cannot be overrided.
13) How
comparison of objects is done in PHP5?
We use the
operator ‘==’ to test is two object are instanced from the same class and have
same attributes and equal values. We can test if two object are refering to the
same instance of the same class by the use of the identity operator ‘===’.
14) How can
PHP and HTML interact?
It is
possible to generate HTML through PHP scripts, and it is possible to pass
informations from HTML to PHP.
15) What
type of operation is needed when passing values through a form or an URL?
If we would
like to pass values througn a form or an URL then we need to encode and to
decode them using htmlspecialchars() and urlencode().
16) How can
PHP and Javascript interact?
PHP and
Javascript cannot directly interacts since PHP is a server side language and
Javascript is a client side language. However we can exchange variables since
PHP is able to generate Javascript code to be executed by the browser and it is
possible to pass specific variables back to PHP via the URL.
17) What is
needed to be able to use image function?
GD library
is needed to be able execute image functions.
18) What is
the use of the function ‘imagetypes()’?
imagetypes()
gives the image format and types supported by the current version of GD-PHP.
19) What are
the functions to be used to get the image’s properties (size, width and
height)?
The
functions are getimagesize() for size, imagesx() for width and imagesy() for
height.
20) How
failures in execution are handled with include() and require() functions?
If the
function require() cannot access to the file then it ends with a fatal error.
However, the include() function gives a warning and the PHP script continues to
execute.
21) What is
the main difference between require() and require_once()?
require()
and require_once() perform the same task except that the second function checks
if the PHP script is already included or not before executing it.
(same for
include_once() and include())
22) How can
I display text with a PHP script?
Two methods
are possible:
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<?php
echo "Method
1";
print "Method
2";
?>
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23) How can
we display information of a variable and readable by human with PHP?
To be able
to display a human-readable result we use print_r().
24) How is
it possible to set an infinite execution time for PHP script?
The
set_time_limit(0) added at the beginning of a script sets to infinite the time
of execution to not have the PHP error ‘maximum execution time exceeded’.It is
also possible to specify this in the php.ini file.
25)
What does the PHP error ‘Parse error in PHP – unexpected T_variable at line x’
means?
This is a
PHP syntax error expressing that a mistake at the line x stops parsing and
executing the program.
26) What
should we do to be able to export data into an Excel file?
The most
common and used way is to get data into a format supported by Excel. For
example, it is possible to write a .csv file, to choose for example comma as
separator between fields and then to open the file with Excel.
27) What is
the function file_get_contents() usefull for?
file_get_contents()
lets reading a file and storing it in a string variable.
28) How can
we connect to a MySQL database from a PHP script?
To be able
to connect to a MySQL database, we must use mysql_connect() function as
follows:
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<?php
$database =
mysql_connect("HOST", "USER_NAME", "PASSWORD");
mysql_select_db("DATABASE_NAME",$database);
?>
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29) What is
the function mysql_pconnect() usefull for?
mysql_pconnect()
ensure a persistent connection to the database, it means that the connection do
not close when the the PHP script ends.
30) How the
result set of Mysql be handled in PHP?
The result
set can be handled using mysql_fetch_array, mysql_fetch_assoc,
mysql_fetch_object or mysql_fetch_row.
31) How is
it possible to know the number of rows returned in result set?
The function
mysql_num_rows() returns the number of rows in a result set.
32) Which
function gives us the number of affected entries by a query?
mysql_affected_rows()
return the number of entries affected by an SQL query.
33) What is
the difference between mysql_fetch_object() and mysql_fetch_array()?
The
mysql_fetch_object() function collects the first single matching record where
mysql_fetch_array() collects all matching records from the table in an array.
34) How can
we access the data sent through the URL with the GET method?
In order to
access the data sent via the GET method, we you use $_GET array like this:
www.url.com?var=value
$variable = $_GET["var"]; this will now contain ‘value’
$variable = $_GET["var"]; this will now contain ‘value’
35) How can
we access the data sent through the URL with the POST method?
To access
the data sent this way, you use the $_POST array.
Imagine you
have a form field called ‘var’ on the form, when the user clicks submit to the
post form, you can then access the value like this:
$_POST["var"];
36) How can
we check the value of a given variable is a number?
It is
possible to use the dedicated function, is_numeric() to check whether it is a
number or not.
37) How can
we check the value of a given variable is alphanumeric?
It is
possible to use the dedicated function, ctype_alpha() to check whether it is an
alphanumeric value or not.
38) How do I
check if a given variable is empty?
If we want
to check whether a variable has a value or not, it is possible to use the
empty() function.
39) What
does the unlink() function means?
The unlink()
function is dedicated for file system handling. It simply deletes the file
given as entry.
40) What
does the unset() function means?
The unlink()
function is dedicated for variable management. It will make a variable
undefined.
41) How do I
escape data before storing it into the database?
addslashes
function enables us to escape data before storage into the database.
42) How is
it possible to remove escape characters from a string?
The
stripslashes function enables us to remove the escape characters before
apostrophes in a string.
43) How can
we automatically escape incoming data?
We have to
enable the Magic quotes entry in the configuration file of PHP.
44) What
does the function get_magic_quotes_gpc() means?
The function
get_magic_quotes_gpc() tells us whether the magic quotes is switched on or no.
45) Is it
possible to remove the HTML tags from data?
The
strip_tags() function enables us to clean a string from the HTML tags.
46) what is
the static variable in function useful for?
A static
variable is defined within a function only the first time and its value can be
modified during function calls as follows:
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<?php
function testFunction()
{ static $testVariable
= 1;
echo $testVariable;
$testVariable++;
}
testFunction();
//1
testFunction();
//2
testFunction();
//3
?>
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47) How can
we define a variable accessible in functions of a PHP script?
This feature
is possible using the global keyword.
48) How is
it possible to return a value from a function?
A function
returns a value using the instruction ‘return $value;’.
49) What is
the most convenient hashing method to be used to hash passwords?
It is
preferable to use crypt() which natively supports several hashing algorithms or
the function hash() which supports more variants than crypt() rather than using
the common hashing algorithms such as md5, sha1 or sha256 because they are
conceived to be fast. hence, hashing passwords with these algorithms can vulnerability.
50) Which
cryptographic extension provide generation and verification of digital
signatures?
The
PHP-openssl extension provides several cryptographic operations including
generation and verification of digital signatures.
51) How a
constant is defined in a PHP script?
The define()
directive lets us defining a constant as follows:
define
(“ACONSTANT”, 123);
52) How can
you pass a variable by reference?
To be able
to pass a variable by reference, we use an ampersand in front of it, as follows
$var1 = &$var2
53) Will a
comparison of an integer 12 and a string “13″ work in PHP?
“13″ and 12
can be compared in PHP since it casts everything to the integer type.
54) How is
it possible to cast types in PHP?
The name of
the output type have to be specified in parentheses before the variable which
is to be cast as follows:
* (int),
(integer) – cast to integer
* (bool),
(boolean) – cast to boolean
* (float),
(double), (real) – cast to float
* (string) –
cast to string
* (array) –
cast to array
* (object) –
cast to object
55) When a
conditional statement is ended with an endif?
When the
original if was followed by : and then the code block without braces.
56) How is
the ternary conditional operator used in PHP?
It is
composed of three expressions: a condition, and two operands describing what
instruction should be performed when the specified condition is true or false
as follows:
Expression_1
? Expression_2 : Expression_3;
57) What is
the function func_num_args() used for?
The function
func_num_args() is used to give the number of parameters passed into a
function.
58) If the
variable $var1 is set to 10 and the $var2 is set to the character var1, what’s
the value of $$var2?
$$var2
contains the value 10.
59) What
does accessing a class via :: means?
:: is used
to access static methods that do not require object initialization.
60) In PHP,
objects are they passed by value or by reference?
In PHP,
objects passed by value.
61) Are
Parent constructors called implicitly inside a class constructor?
No, a parent
constructor have to be called explicitly as follows:
parent::constructor($value)
62) What’s
the difference between __sleep and __wakeup?
__sleep
returns the array of all the variables that need to be saved, while __wakeup
retrieves them.
63) What is
faster?
1- Combining
two variables as follows:
$variable1 =
‘Hello ‘;
$variable2 =
‘World’;
$variable3 =
$variable1.$variable2;
Or
2-
$variable3 = “$variable1$variable2″;
$variable3
will contain “Hello World”. The first code is faster than the second code especially
for large large sets of data.
64) what is
the definition of a session?
A session is
a logical object enabling us to preserve temporary data across multiple PHP
pages.
65) How to
initiate a session in PHP?
The use of
the function session_start() lets us activating a session.
66) How is
it possible to propagate a session id?
It is
possible to propagate a session id via cookies or URL parameters.
67) What is
the meaning of a Persistent Cookie?
A persistent
cookie is permanently stored in a cookie file on the browser’s computer. By
default, cookies are temporary and are erased if we close the browser.
68) When
sessions ends?
Sessions
automatically ends when the PHP script finishs executing, but can be manually
ended using the session_write_close().
69) What is
the difference between session_unregister() and session_unset()?
The
session_unregister() function unregister a global variable from the current
session and the session_unset() function free all session variables.
70) What
does $GLOBALS means?
$GLOBALS is
associative array including references to all variables which are currently
defined in the global scope of the script.
71) What
does $_SERVER means?
$_SERVER is
an array including information created by the web server such as paths,
headers, and script locations.
72) What
does $_FILES means?
$_FILES is
an associative array composed of items sent to the current script via the HTTP
POST method.
73) What is
the difference between $_FILES['userfile']['name'] and
$_FILES['userfile']['tmp_name']?
$_FILES['userfile']['name']
represents the original name of the file on the client machine,
$_FILES['userfile']['tmp_name']
represents the temporary filename of the file stored on the server.
74) How can
we get the error when there is a problem to upload a file?
$_FILES['userfile']['error']
contains the error code associated with the uploaded file.
75) How can
we change the maximum size of the files to be uploaded?
We can
change the maximum size of files to be uploaded by changing upload_max_filesize
in php.ini.
76) What
does $_ENV means?
$_ENV is an
associative array of variables sent to the current PHP script via the
environment method.
77) What
does $_COOKIE means?
$_COOKIE is
an associative array of variables sent to the current PHP script using the HTTP
Cookies.
78) What
does the scope of variables means?
The scope of
a variable is the context within which it is defined. For the most part all PHP
variables only have a single scope. This single scope spans included and
required files as well.
79) what the
difference between the ‘BITWISE AND’ operator and the ‘LOGICAL AND’ operator?
$a and
$b: TRUE if both $a and $b are TRUE.
$a &
$b: Bits that are set in both $a and
$b are set.
80) What are
the two main string operators?
The first is
the concatenation operator (‘.’), which returns the concatenation of its right
and left arguments. The second is (‘.=’), which appends the argument on the
right to the argument on the left.
81) What
does the array operator ‘===’ means?
$a === $b
TRUE if $a and $b have the same key/value pairs in the same order and of the
same types.
82) What is
the differences between $a != $b and $a !== $b?
!= means
inequality (TRUE if $a is not equal to $b) and !== means non-identity (TRUE if
$a is not identical to $b).
83) How can
we determine whether a PHP variable is an instantiated object of a certain
class?
To be able
to verify whether a PHP variable is an instantiated object of a certain class
we use instanceof.
84) What is
the goto statement useful for?
The goto
statement can be placed to enable jumping inside the PHP program. The target is
pointed by a label followed by a colon, and the instruction is specified as a
goto statement followed by the desired target label.
85) what is
the difference between Exception::getMessage and Exception::getLine ?
Exception::getMessage
lets us getting the Exception message and Exception::getLine lets us getting
the line in which the exception occurred.
86) What
does the expression Exception::__toString means?
Exception::__toString
gives the String representation of the exception.
87) How is
it possible to parse a configuration file?
The function
parse_ini_file() enables us to load in the ini file specified in filename, and
returns the settings in it in an associative array.
88) How can
we determine whether a variable is set?
The boolean
function isset determines if a variable is set and is not NULL.
89) What is
the difference between the functions strstr() and stristr()?
The string
function strstr(string allString, string occ) returns part of allString from
the first occurrence of occ to the end of allString. This function is
case-sensitive. stristr() is identical to strstr() except that it is case
insensitive.
90) what is
the difference between for and foreach?
for is expressed
as follows:
for (expr1;
expr2; expr3)
statement
The first
expression is executed once at the beginning. In each iteration, expr2 is
evaluated. If it is TRUE, the loop continues and the statements inside for are
executed. If it evaluates to FALSE, the execution of the loop ends. expr3 is
tested at the end of each iteration.
However,
foreach provides an easy way to iterate over arrays and it is only used with
arrays and objects.
91) Is it
possible to submit a form with a dedicated button?
It is
possible to use the document.form.submit() function to submit the form. For
example: <input type=button value=”SUBMIT”
onClick=”document.form.submit()”>
92) What is
the difference between ereg_replace() and eregi_replace()?
The function
eregi_replace() is identical to the function ereg_replace() except that it
ignores case distinction when matching alphabetic characters.
93) Is it
possible to protect special characters in a query string?
Yes, we use
the urlencode() function to be able to protect special characters.
94) What are
the three classes of errors that can occur in PHP?
The three
basic classes of errors are notices (non-critical), warnings (serious errors)
and fatal errors (critical errors).
95) What is
the difference between characters \034 and \x34?
\034 is
octal 34 and \x34 is hex 34.
96) How can
we pass the variable through the navigation between the pages?
It is
possible to pass the variables between the PHP pages using sessions, cookies or
hidden form fields.
97) Is it
possible to extend the execution time of a php script?
The use of
the set_time_limit(int seconds) enables us to extend the execution time of a
php script. The default limit is 30 seconds.
98) Is it
possible to destroy a cookie?
Yes, it is
possible by setting the cookie with a past expiration time.
99) What is
the default session time in php?
The default
session time in php is until closing of browser
100) Is it
possible to use COM component in PHP?
Yes, it’s
possible to integrate (Distributed) Component Object Model components ((D)COM)
in PHP scripts which is provided as a framework.
Read
more at http://www.gointerviews.com/top-100-php-interview-questions-answers/#BIPMwTO3RAdUUX4g.99
