PHP interview questions and answers

PHP,PHP questions, answer,Technical PHP interview questions,PHP interview, PHP job questions

1. How can we extract string 'abc.com ' from a string 'http://info@a...' using regular _expression of php?

Ans : We can use the preg_match() function with "/.*@(.*)$/" as the regular expression pattern. For example: preg_match("/.*@(.*)$/","http://info@abc.com",$data); echo $data[1];

2. What are the different tables present in mysql ?
Ans : 1. MyISAM
2. Heap
3. Merge
4. InnoDB
5. ISAM
6. BDB

3. How can I execute a php script using command line?
Ans : Just run the PHP CLI (Command Line Interface) program and provide the PHP script file name as the command line argument. For example, "php myScript.php", assuming "php" is the command to invoke the CLI program.
Be aware that if your PHP script was written for the Web CGI interface, it may not execute properly in command line environment.

4. What is meant by nl2br() ?
Ans : nl2br -- Inserts HTML line breaks before all newlines in a string
string nl2br (string); Returns string with '
' inserted before all newlines.
For example: echo nl2br("god bless\n you") will output "god bless
\n you" to your browser.

5. How can we encrypt and decrypt a data present in a mysql table using mysql?
Ans :AES_ENCRYPT () and AES_DECRYPT () .

6. What are the features and advantages of OBJECT ORIENTED PROGRAMMING ?
Ans : One of the main advantages of OO programming is its ease of modification; objects can easily be modified and added to a system there by reducing maintenance costs. OO programming is also considered to be better at modeling the real world than is procedural programming. It allows for more complicated and flexible interactions. OO systems are also easier for non-technical personnel to understand and easier for them to participate in the maintenance and enhancement of a system because it appeals to natural human cognition patterns.
For some systems, an OO approach can speed development time since many objects are standard across systems and can be reused. Components that manage dates, shipping, shopping carts, etc. can be purchased and easily modified for a specific system.

7. What are the differences between PROCEDURE ORIENTED LANGUAGES
AND OBJECT ORIENTED LANGUAGES?
Ans :Traditional programming has the following characteristics:
Functions are written sequentially, so that a change in programming can affect any code that follows it.
If a function is used multiple times in a system (i.e., a piece of code that manages the date), it is often simply cut and pasted into each program (i.e., a change log, order function, fulfillment system, etc). If a date change is needed (i.e., Y2K when the code needed to be changed to handle four numerical digits instead of two), all these pieces of code must be found, modified, and tested.
Code (sequences of computer instructions) and data (information on which the instructions operates on) are kept separate. Multiple sets of code can access and modify one set of data. One set of code may rely on data in multiple places. Multiple sets of code and data are required to work together. Changes made to any of the code sets and data sets can cause problems through out the system.
Object-Oriented programming takes a radically different approach:
Code and data are merged into one indivisible item – an object (the term “component” has also been used to describe an object.) An object is an abstraction of a set of real-world things (for example, an object may be created around “date”) The object would contain all information and functionality for that thing (A date
object it may contain labels like January, February, Tuesday, Wednesday. It may contain functionality that manages leap years, determines if it is a business day or a holiday, etc., See Fig. 1). Ideally, information about a particular thing should reside in only one place in a system. The information within an object is encapsulated (or hidden) from the rest of the system.
A system is composed of multiple objects (i.e., date function, reports, order processing, etc., See Fig 2). When one object needs information from another object, a request is sent asking for specific information. (for example, a report object may need to know what today’s date is and will send a request to the date object) These requests are called messages and each object has an interface that manages messages.
OO programming languages include features such as “class”, “instance”, “inheritance”, and “polymorphism” that increase the power and flexibility of an object.

8. What is the use of friend function?
Ans : Sometimes a function is best shared among a number of different classes. Such functions can be declared either as member functions of one class or as global functions. In either case they can be set to be friends of other classes, by using a friend specifier in the class that is admitting them. Such functions can use all attributes of the class whichnames them as a friend, as if they were themselves members of that class.
A friend declaration is essentially a prototype for a member function, but instead of requiring an implementation with the name of that class attached by the double colon syntax, a global function or member function of another class provides the match.
class mylinkage {
private:
mylinkage * prev;
mylinkage * next;
protected:
friend void set_prev(mylinkage* L, mylinkage* N);
void set_next(mylinkage* L);
public:
mylinkage * succ();
mylinkage * pred();
mylinkage();
};
void mylinkage::set_next(mylinkage* L) { next = L; }
void set_prev(mylinkage * L, mylinkage * N ) { N->prev = L; }
Friends in other classes
It is possible to specify a member function of another class as a friend as follows:
class C {
friend int B::f1();
};
class B {
int f1();
};
It is also possible to specify all the functions in another class as friends, by specifying the entire class as a friend.
class A {
friend class B;
};
Friend functions allow binary operators to be defined which combine private data in a pair of objects. This is particularly powerful when using the operator overloading features of C++. We will return to it when we look at overloading.

9. What are the different types of errors in php?
Ans: Three are three types of errors:
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, as you will see, you can change this default behaviour.
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 behaviour is to display them to the user when they take place.

10. What is the functionality of the function strstr and stristr ?
Ans: strstr() returns part of a given string from the first occurrence of a given substring to the end of the string. For example: strstr("user@example.com","@") will return "@example.com".
stristr() is idential to strstr() except that it is case insensitive.

11 . What is the functionality of the function htmlentities?
Ans :htmlentities -- Convert all applicable characters to HTML entities
This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.

12 . How can we convert the time zones using php?
echo "Original Time: ". date("h:i:s")."\n";
putenv("TZ=US/Eastern");
echo "New Time: ". date("h:i:s")."\n";

13. What is meant by urlencode and urldocode?
Ans: urlencode() returns the URL encoded version of the given string. URL coding converts special characters into % signs followed by two hex digits. For example: urlencode("10.00%") will return "10%2E00%25". URL encoded strings are safe to be used as part of URLs.
urldecode() returns the URL decoded version of the given string.

14.What is the difference between the functions unlink and unset?
unlink() deletes the given file from the file system.
unset() makes a variable undefined.

15 . How can we get the properties (size, type, width, height) of an image using php image functions?
Ans :To know the Image type use exif_imagetype () function
To know the Image size use getimagesize () function
To know the image width use imagesx () function
To know the image height use imagesy() function

16.How can we get the browser properties using php?
Ans : echo $_SERVER['HTTP_USER_AGENT'] . "\n\n";
$browser = get_browser(null, true);
print_r($browser);
What is the maximum size of a file that can be uploaded using php and how can we change this?
You can change maximum size of a file set upload_max_filesize variable in php.ini file

17.How can we increase the execution time of a php script?
Set max_execution_time variable in php.ini file to your desired time in second.

18. How can we take a backup of a mysql table and how can we restore it.?

Create a full backup of your database: shell> mysqldump --tab=/path/to/some/dir --opt db_name Or: shell> mysqlhotcopy db_name /path/to/some/dir

The full backup file is just a set of SQL statements, so restoring it is very easy:

shell> mysql <>

19. How can we optimize or increase the speed of a mysql select query?
Ans : In general, when you want to make a slow SELECT … WHERE query faster, the first thing to check is whether you can add an index. All references between different tables should usually be done with indexes. You can use the EXPLAIN statement to determine which indexes are used for a SELECT.
Some general tips for speeding up queries on MyISAM tables:
A: To help MySQL better optimize queries, use ANALYZE TABLE or run myisamchk --analyze on a table after it has been loaded with data. This updates a value for each index part that indicates the average number of rows that have the same value. (For unique indexes, this is always 1.) MySQL uses this to decide which index to choose when you join two tables based on a non-constant expression. You can check the result from the table analysis by using SHOW INDEX FROM tbl_name and examining the Cardinality value. myisamchk --description --verbose shows index distribution information.

20 . How can we destroy the session, how can we unset the variable of a session?

Ans :session_unregister() unregisters a global variable from the current session.

session_unset() frees all session variables.

21. How many ways we can pass the variable through the navigation between the pages?

a) Register the variable into the session

b) Pass the variable as a cookie

c) Pass the variable as part of the URL

22.What is the difference between ereg_replace() and eregi_replace()?

eregi_replace() function is identical to ereg_replace() except that this ignores case distinction when matching alphabetic characters.

23 What are the different functions in sorting an array?
Sorting functions in PHP:
asort()
arsort()
ksort()
krsort()
uksort()
sort()
natsort()
rsort()

24. How can we know the count/number of elements of an array?
a) sizeof($urarray) This function is an alias of count()
b) count($urarray)
Interestingly if u just pass a simple var instead of a an array it will return 1.

25 What is the php predefined variable that tells the What types of images that php supports?

Ans :$_SERVER['HTTP_ACCEPT']

26. How can I know that a variable is a number or not using a _JavaScript?
Ans :function IsNumeric(sText)
{
var ValidChars = "0123456789.";
var IsNumber=true;
var Char;
for (i = 0; i < isnumber ="=">
{
Char = sText.charAt(i);
if (ValidChars.indexOf(Char) == -1)
{
IsNumber = false;
}
}
return IsNumber;
}

27. List out the predefined classes in php?

Ans : stdClass

__PHP_Incomplete_Class

exception

php_user_filter

28. What are the difference between abstract class and interface?
Ans : Abstract class: abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.Interface: Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be define by its implemented class.

29.What are the advantages of stored procedures, triggers, indexes?
A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep re-issuing the entire query but can refer to the stored procedure. This provides better overall performance because the query has to be parsed only once, and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server. However, stored procedures of course do increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side.
Triggers will also be implemented. A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.
Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. If you need to access most of the rows, it is faster to read sequentially, because this minimizes disk seeks.
30. What is the maximum length of a table name, database name, and fieldname in mysql?
Database name- 64
Table name -64
Fieldname-64

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