December 02, 2019

Top 20 PHP Interview Questions and Answers

Ques: 1) What is CAPTCHA?


CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Humans Apart. To prevent spammers from using bots to automatically fill out forms, CAPTCHA programmers will generate an image containing distorted images of a string of numbers and letters. Computers cannot determine what the numbers and letters are from the image but humans have great pattern recognition abilities and will be able to fairly accurately determine the string of numbers and letters. By entering the numbers and letters from the image in the validation field, the application can be fairly assured that there is a human client using it.


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Ques: 2) What is meant by urlencode() and urldecode()?


string urlencode(str)

When str contains a string like this “hello world” and the return value will be URL encoded and can be use to append with URLs, normally used to append data for GET like

string urldocode(str)

This will simple decode the GET variable’s value. Example: echo (urldecode($_GET_VARS[var])) will output “hello world”


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Ques: 3) What is difference between mysql_fetch_array(), mysql_fetch_row() and mysql_fetch_object()?


mysql_fetch_array - Fetch the all matching records of results.

mysql_fetch_object - Fetch the first single matching record of results.

mysql_fetch_row - fetches a result row as array.


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Ques: 4) What is difference between srand & shuffle?


The srand function seeds the random number generator with seed and shuffle is used for shuffling the array values.

shuffle - This function shuffles (randomizes the order of the elements in) an array. This function assigns new keys for the elements in array. It will remove any existing keys you may have assigned, rather than just reordering the keys.

srand - Seed the random number generator


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Ques: 5) How do you capture audio/video in PHP?


You need a module installed - FFMPEG. FFmpeg is a complete solution to record, convert and stream audio and video. It includes libavcodec, the leading audio/video codec library. FFmpeg is developed under Linux, but it can be compiled under most operating systems, including Windows.


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Ques: 6) What's the difference between COPY OF A FILE & MOVE_UPLOAD_FILE in file uploading?


Move: This function checks to ensure that the file designated by filename is a valid upload file (meaning that it was uploaded via PHP's HTTP POST upload mechanism). If the file is valid, it will be moved to the filename given by destination.

If filename is not a valid upload file, then no action will occur, and move_uploaded_file() will return FALSE.

Copy: Makes a copy of a file. Returns TRUE if the copy succeeded, FALSE otherwise.


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Ques: 7) What is the difference between echo and print?


Main difference between echo() and print() is that echo is just an statement not a function and doesn't return's value or it just prints a value whereas print() is an function which prints a value and also it returns value.

We cannot pass arguments to echo since it is just a statement whereas print is a function and we can pass arguments to it and it returns true or false. print can be used as part of a more complex expression whereas echo cannot. echo is marginally faster since it doesn't set a return value.


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Ques: 8) What is the difference between require() and include()?


Both of these constructs includes and evaluates the specific file. The two functions are identical in every way except how they handle failure. If filepath not found, require() terminates the program and gives fatal error, but include() does not terminate the program; It gives warning message and continues to program.

include() produces a Warning while require() results in a Fatal Error if the filepath is not correct.


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Ques: 9) How do we know properties of the browser?


You can gather a lot of information about a person's computer by using $_SERVER['HTTP_USER_AGENT']. This can tell us more about the user's operating system, as well as their browser. For example I am revealed to be Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/418 (KHTML, like Gecko) Safari/417.9.3 when visiting a PHP page.

This can be useful to programmers if they are using special features that may not work for everyone, or if they want to get an idea of their target audience. This also is important when using the get_browser() function for finding out more information about the browser's capabilities. By having this information the user can be directed to a version of your site best suited to their browser.

get_browser() attempts to determine the capabilities of the user's browser. This is done by looking up the browser's information in the browscap.ini file.

echo $_SERVER['HTTP_USER_AGENT'] . "<hr />\n";

$browser = get_browser();

foreach ($browser as $name => $value)  { echo "<b>$name</b> $value <br />\n";



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Ques: 10) What is difference between require_once(), require(), include(). Because all these function are used to call a file in another file.


Difference between require() and require_once(): require() includes and evaluates a specific file, while require_once() does that only if it has not been included before (on the same page).

So, require_once() is recommended to use when you want to include a file where you have a lot of functions for example. This way you make sure you don't include the file more times and you will not get the "function re-declared" error.

Difference between require() and include() is that require() produces a FATAL ERROR if the file you want to include is not found, while include() only produces a WARNING.

There is also include_once() which is the same as include(), but the difference between them is the same as the difference between require() and require_once().


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Ques: 11) What are 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. By default, such errors are not displayed to the user at all - although you can change this default behavior.

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.


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Ques: 12) How to Create a Cookie & destroy it in PHP?



variable - name of the cookie variable variable - value of the cookie variable time - expiry time

Example: setcookie(”test”,$i,time()+3600);

Test - cookie variable name

$i - value of the variable ‘Test’ time()+3600 - denotes that the cookie will expire after an one hour.

Destroy a cookie by specifying expiry time

Example: setcookie(”test”,$i,time()-3600); // already expired time

Reset a cookie by specifying its name only



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Ques: 13) What is the difference between the functions unlink and unset?


unlink is a function for file system handling. It will simply delete the file in context. unset will set UNSET the specified variable.

unlink is used to delete a file. unset is used to destroy an earlier declared variable.


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Ques: 14) How do you know (status) whether the recipient of your mail had opened the mail i.e. read the mail?


Embed an URL in a say 0-byte image tag may be the better way to go. In other word, you embed an invisible image on you html email and when the src URL is being rendered by the server, you can track whether your recipients have view the emails or not.


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Ques: 15) What is difference between mysql_connect and mysql_pconnect?


mysql_connect opens up a database connection every time a page is loaded. mysql_pconnect opens up a connection, and keeps it open across multiple requests.

mysql_pconnect uses less resources, because it does not need to establish a database connection every time a page is loaded.


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Ques: 16) What do you need to do to improve the performance (speedy execution) for the script you have written?


If your script is to retrieve data from Database, you should use "Limit" syntax. Break down the non dynamic sections of website which need not be repeated over a period of time as include files.


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Ques: 17) How do you insert single & double quotes in MySQL db without using PHP?


By using &amp; / &quote;

Alternately, escape single quote using forward slash \' . In double quote you don't need to escape quotes. Insert double quotes as "".


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Ques: 18) What is the difference between strstr & stristr?


For strstr, the syntax is: string strstr(string $string,string $str ); The function strstr will search $str in $string. If it finds the string means it will return string from where it finds the $str upto end of $string.

For Example:

$string = ""; $str="yahoomail";

The output is "". The main difference between strstr and stristr is of case sensitivity. The former consider the case difference and later ignore the case difference.


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Ques: 19) What is the difference between explode and split?


Split function splits string into array by regular expression. Explode splits a string into array by string.

For Example:

explode(" and", "India and Pakistan and Srilanka"); split(" :", "India : Pakistan : Srilanka");

Both of these functions will return an array that contains India, Pakistan, and Srilanka.


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Ques: 20) How can you avoid execution time out error while fetching record from MySQL?


set_time_limit -- Limits the maximum execution time

For Example:


If you set to 0 you say that there is not limit.


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