Interview Questions - 3 - PHP - Answers

Back - Interview Questions - 3

1. Ans - Crypto usage in PHP is simple, but that doesn’t mean it’s free. First off, depending on the data that you’re encrypting, you might have reasons to store a 32-bit value in the database instead of the 160-bit value to save on space. Second, the more secure the crypto is, the longer is the computation time to deliver the hash value. A high volume site might be significantly slowed down, if frequent md5() generation is required.

2. Ans - htmlspecialchars only takes care of <, >, single quote ‘, double quote " and ampersand. htmlentities translates all occurrences of character sequences that have different meaning in HTML.

3. Ans - The major difference is the length of the hash generated. CRC32 is, evidently, 32 bits, while sha1() returns a 128 bit value, and md5() returns a 160 bit value. This is important when avoiding collisions.

4. Ans - ASSIGNMENTSSTORE IS COLLECTION OF INTERVIEW QUESTIONS. ucwords() makes every first letter of every word capital, but it does not lower-case anything else. To avoid this, and get a properly formatted string, it’s worth using strtolower() first

5. Ans - On large strings that need to be formatted according to some length specifications, use wordwrap() or chunk_split() 

6. Ans - Both examples would provide the same result - $var3 equal to "Welcome to Assignmentsstore.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution. 

7. Ans - echo is the most primitive of them, and just outputs the contents following the construct to the screen. print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. However, you can pass multiple parameters to echo, like: 
 <?php echo 'Welcome ', 'to', ' ', 'Assignmentsstore!'; ?> 
and it will output the string "Welcome to Assignmentsstore!" print does not take multiple parameters. It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP. printf  is a function, not a construct, and allows such advantages as formatted output, but it’s the slowest way to print out data out of echo, print and printf.

8. Ans - 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.

9. Ans

$date1 = date('Y-m-d');
$date2 = '2015-07-01'; 

$days = (strtotime() - strtotime()) / (60 * 60 * 24); 

echo "Number of days since '2015-07-01': $days";

10. Ans. 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.