Daum PHP Most Frequently Asked Latest Interview Questions Answers
How To Close A Session Properly?
Let's say you site requires users to login. When a logged in user clicks the logout button, you need to close the session associated with this user properly in 3 steps:
1. Remove all session values with $_SESSION = array().
2. Remove the session ID cookie with the setcookie() function.
3. Destroy the session object with the session_destroy() function.
Below is a good sample script:
<?php
session_start();
$_SESSION = array();
if (isset($_COOKIE[session_name()])) {
setcookie(session_name(), '', time()-42000, '/');
}
session_destroy();
print("<html><pre>");
print("Thank you for visiting PICKZYCenter.com.\n");
print(" <a href=login.php>Login Again.</a>\n");
print("</pre></html>\n");
?>
Just use the PHP command line interface (CLI) and specify the file name of the script to be executed as follows:
php script.php
How can PHP and HTML interact?
It is possible to generate HTML through PHP scripts, and it is possible to pass pieces of information from HTML to PHP.
What type of operation is needed when passing values through a form or an URL?
If we would like to pass values through a form or an URL, then we need to encode and to decode them using htmlspecialchars() and urlencode().
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.
How can we check the value of a given variable is alphanumeric?
It is possible to use the dedicated function, ctype_alnum to check whether it is an alphanumeric value or not.
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.
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.
How failures in execution are handled with include() and require() functions?
If the function require() cannot access the file then it ends with a fatal error. However, the include() function gives a warning, and the PHP script continues to execute.
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())
How can I display text with a PHP script?
Two methods are possible:
<!--?php echo "Method 1"; print "Method 2"; ?-->
How can we display information of a variable and readable by a human with PHP?
To be able to display a human-readable result we use print_r().
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.
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.
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 a separator between fields and then to open the file with Excel.
What is the function file_get_contents() useful for?
file_get_contents() lets reading a file and storing it in a string variable.
How can we connect to a MySQL database from a PHP script?
To be able to connect to a MySQL database, we must use mysqli_connect() function as follows:
<!--?php $database = mysqli_connect("HOST", "USER_NAME", "PASSWORD"); mysqli_select_db($database,"DATABASE_NAME"); ?-->
What is the function mysql_pconnect() useful for?
mysql_pconnect() ensure a persistent connection to the database, it means that the connection does not close when the PHP script ends.
This function is not supported in PHP 7.0 and above
How be the result set of Mysql handled in PHP?
The result set can be handled using mysqli_fetch_array, mysqli_fetch_assoc, mysqli_fetch_object or mysqli_fetch_row.
How is it possible to know the number of rows returned in the result set?
The function mysqli_num_rows() returns the number of rows in a result set.
The unlink() function is dedicated for file system handling. It simply deletes the file given as entry.
What does the unset() function mean?
The unset() function is dedicated for variable management. It will make a variable undefined.
How do I escape data before storing it in the database?
The addslashes function enables us to escape data before storage into the database.
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.
How can we automatically escape incoming data?
We have to enable the Magic quotes entry in the configuration file of PHP.
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.
Is it possible to remove the HTML tags from data?
The strip_tags() function enables us to clean a string from the HTML tags.
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:
<!--?php function testFunction() { static $testVariable = 1; echo $testVariable; $testVariable++; } testFunction(); //1 testFunction(); //2 testFunction(); //3 ?-->
How is it possible to cast types in PHP?
The name of the output type has 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
When is a conditional statement ended with endif?
When the original if was followed by: and then the code block without braces.
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;
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.
How can we define a variable accessible in functions of a PHP script?
This feature is possible using the global keyword.
How is it possible to return a value from a function?
A function returns a value using the instruction 'return $value;'.
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 create vulnerability.
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.
Explain how you can update Memcached when you make changes to PHP?
When PHP changes you can update Memcached by
Clearing the Cache proactively: Clearing the cache when an insert or update is made
Resetting the Cache: It is similar to the first method but rather than just deleting the keys and waiting for the next request for the data to refresh the cache, reset the values after the insert or update.
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.
How is a constant defined in a PHP script?
The define() directive lets us defining a constant as follows:
define ("ACONSTANT", 123);
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
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.
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.
How To Close A Session Properly?
Let's say you site requires users to login. When a logged in user clicks the logout button, you need to close the session associated with this user properly in 3 steps:
1. Remove all session values with $_SESSION = array().
2. Remove the session ID cookie with the setcookie() function.
3. Destroy the session object with the session_destroy() function.
Below is a good sample script:
<?php
session_start();
$_SESSION = array();
if (isset($_COOKIE[session_name()])) {
setcookie(session_name(), '', time()-42000, '/');
}
session_destroy();
print("<html><pre>");
print("Thank you for visiting PICKZYCenter.com.\n");
print(" <a href=login.php>Login Again.</a>\n");
print("</pre></html>\n");
?>
 |
| Daum PHP Most Frequently Asked Latest Interview Questions Answers |
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:
php script.php
How can PHP and HTML interact?
It is possible to generate HTML through PHP scripts, and it is possible to pass pieces of information from HTML to PHP.
What type of operation is needed when passing values through a form or an URL?
If we would like to pass values through a form or an URL, then we need to encode and to decode them using htmlspecialchars() and urlencode().
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.
How can we check the value of a given variable is alphanumeric?
It is possible to use the dedicated function, ctype_alnum to check whether it is an alphanumeric value or not.
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.
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.
How failures in execution are handled with include() and require() functions?
If the function require() cannot access the file then it ends with a fatal error. However, the include() function gives a warning, and the PHP script continues to execute.
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())
How can I display text with a PHP script?
Two methods are possible:
<!--?php echo "Method 1"; print "Method 2"; ?-->
How can we display information of a variable and readable by a human with PHP?
To be able to display a human-readable result we use print_r().
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.
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.
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 a separator between fields and then to open the file with Excel.
What is the function file_get_contents() useful for?
file_get_contents() lets reading a file and storing it in a string variable.
How can we connect to a MySQL database from a PHP script?
To be able to connect to a MySQL database, we must use mysqli_connect() function as follows:
<!--?php $database = mysqli_connect("HOST", "USER_NAME", "PASSWORD"); mysqli_select_db($database,"DATABASE_NAME"); ?-->
What is the function mysql_pconnect() useful for?
mysql_pconnect() ensure a persistent connection to the database, it means that the connection does not close when the PHP script ends.
This function is not supported in PHP 7.0 and above
How be the result set of Mysql handled in PHP?
The result set can be handled using mysqli_fetch_array, mysqli_fetch_assoc, mysqli_fetch_object or mysqli_fetch_row.
How is it possible to know the number of rows returned in the result set?
The function mysqli_num_rows() returns the number of rows in a result set.
What does the unlink() function mean?
The unlink() function is dedicated for file system handling. It simply deletes the file given as entry.
What does the unset() function mean?
The unset() function is dedicated for variable management. It will make a variable undefined.
How do I escape data before storing it in the database?
The addslashes function enables us to escape data before storage into the database.
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.
How can we automatically escape incoming data?
We have to enable the Magic quotes entry in the configuration file of PHP.
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.
Is it possible to remove the HTML tags from data?
The strip_tags() function enables us to clean a string from the HTML tags.
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:
<!--?php function testFunction() { static $testVariable = 1; echo $testVariable; $testVariable++; } testFunction(); //1 testFunction(); //2 testFunction(); //3 ?-->
How is it possible to cast types in PHP?
The name of the output type has 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
When is a conditional statement ended with endif?
When the original if was followed by: and then the code block without braces.
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;
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.
How can we define a variable accessible in functions of a PHP script?
This feature is possible using the global keyword.
How is it possible to return a value from a function?
A function returns a value using the instruction 'return $value;'.
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 create vulnerability.
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.
Explain how you can update Memcached when you make changes to PHP?
When PHP changes you can update Memcached by
Clearing the Cache proactively: Clearing the cache when an insert or update is made
Resetting the Cache: It is similar to the first method but rather than just deleting the keys and waiting for the next request for the data to refresh the cache, reset the values after the insert or update.
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.
How is a constant defined in a PHP script?
The define() directive lets us defining a constant as follows:
define ("ACONSTANT", 123);
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
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.
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.