Wednesday, 31 July 2013

ERROR CODE MEANING







  





































































































































































































































100

Continue. Request initiated and not rejected. The client can continue.

101

Switching Protocols. The server reports having received a request to change protocol and it is accepted.

102

In processing. Makes clear that the server is active and not inaccessible.(WebDav Extension).



Request processed


200

Request completed successfully.The page is found and displayed.

201

Created.Establishing a link between the client and the server in the form of URI on a newly created resource.

202

Accepted.The request is received and accepted but not yet processed..

203

Non-Authoritative information.The server
response provides information that does not certify it. It could come
from a third-party source.

204

No content.No information to return from the server.

205

Reset content. Request processed, the client
must reset the source of the request.In the case of a form, it must be
cleared before another request.

206

Partial content.Only part of the content is
returned.(This may be due to limitation of resources). A Range header
must have been included by the user.

207

Multiple statements for the answer.(WebDav Extension).

210

Different contents between the server and the client.(WebDav Extension).



Redirections


300

Multiple choice.The server has different answers, so it must return a list of resources with their location.

301

Moved permanently.To be used when a file is
renamed or moved, and a new URL must be provided.The old URL will be
ignored by robots.

302

Moved temporarily. A new URL is provided but robots return to the original URL.

303

See other location.This code is returned
when the resource can be retrieved atto another address and a GET method
must be used to obtain it. The client is redirected if the method is
GET.

304

Unmodified.The page has not changed since
the last request, and no content is returned.This assumes that the
server is configured to provide a If-modified-since header.

Essential for robots of search engines.

305

Use a proxy.Response from the server asking to recover the document on a proxy server whose address is provided.

307

Temporary redirect.The request is redirected to another address as 302.



Client error or access denied


400

Bad request.The server does not recognize the command syntax.

401

Unauthorized.Authentication required. Connections refused unless a valid password is furnished.

402

Payment required. Future use.

403

Forbidden.Access is prohibited or it is prohibited to a specified robot (for the server and not by robots.txt).

404

Not found.The page does not exist.This may be due to an incorrect spelling, different cases on Unix, or a change of address.

405

Method of request not allowed.

406

Not acceptable.The server can not provide the type of document requested.

407

Proxy authentication required.The connection
is refused because the client needs to connect only through a proxy
server that is indicated in the response.

408

Timeout. Expiration of time allocated to a request.

409

Conflict.The request contains a request that
conflicts with the state of the resource. The information on the causes
are provided with the error code. Occurs with the PUT method.

410

Gone.As 404 but means that the page not
found was there before. Google recommends its use rather than 404 when
the page is missing forever.

411

Length required.The server does not accept the request if the Content-Length is not specified.

412

Precondition not met.The request is accompanied by conditions that the server can not fulfill.

413

Volume asked too high.The server can not provide a document of this size.

414

Request-URI too long.The size of the URI
sent to the server exceeds the number of characters allowed. Occurs whan
a POST is converted to GET.

415

Unsupported media type.The client requests a document type that the server does not support.

416

Requested range not satisfiable. The request
specifies the Range (ex 200-10000) and the size of the resource is not
included in this range.

417

Expectation failed .The request contains a field Expect and the server can not meet it.The definition of this field is vague.

422

The request contains an entity that the server can not handle.(WebDav Extension).

423

Locked.The page is locked and will not be transmitted.(WebDav Extension).

424

Failure of the method used by the request.(WebDav Extension).



Server errors


500

Internal Server Error.The request is not processed.

501

Not implemented.The server does not recognize the nature of the request, the method used, for example.

502

Bad gateway.When the server acts as a proxy or intermediary and that the other server not responding.

503

Service unavailable.Temporary problem due to overloading or other server problem including maintenance.

504

Gateway timeout. Waiting time from the other server exceeded, when the server asked plays the role of gateway.

505

HTTP Version not supported.The protocol used is too recent or not handled.

507

Space on the server insufficient to accomplish the client's request.(WebDav Extension).

509

Non-standard code but may be used by servers when exceeding quota.  








History of C++



History of C++

              In 1960sdifferent languages were used for different applications, for example, FORTRANfor Engineering Application, COBOL for Commercial Application and so on. Later on an international committee was set up that developed a single language called ALGOL 60, Which can be used for all application. But this language was too abstract and too general to be accepted. This lead to the development of a new language named CPL ( Combined Programming Language), which had so many features and was hard to learn and implement. After this Martin Richards BCPL(Basic Combined Programming Language) and Ken Thompson’s B language were also not accepted because they were too specific to be implemented. Finally, in 1972, Ritchie made a successful attempt at AT&T’s Bell Laboratories of USAto develop a new language called C language by inheriting the features of both the BCPL and B languages. In order to define the C language, a committee was set up to create an ANSI (American National Standards Institute) standard called ANSI C standard, which was finally adopted by ISO (International Standard Organization) in 1989.

                      Bjarne Stroustrup ar Bell Labs initially developed C++ during the early 1980’s. it was designed to support the features of C such as efficiency and low-level support for system level coding. Added to this were features such as classes with inheritance and virtual functions. C++ is best described as a superset of C, with full support for object-oriented programming. Though C is an excellent language for writing efficient system programs, but for other types of programs, C code can be hard to understand, C programs can also be prone to certain types of error. The extra object-oriented facilities in C++ are partly included to overcome these shortcomings.

Tuesday, 30 July 2013

OPERATING SYSTEM, Types of OPERATING SYSTEM

OPERATING SYSTEM
An operating system is defined as an interface (or bridge) between the user of computer and the computer hardware. An operating creates such a friendly environment for the user in which the computer is used effectively and efficiently. An operating system performs a number inter-process communication, protection and security.

Types of OPERATING SYSTEM
BATCH PROCESSING OPERATING SYSTEM
       Batch processing means executing a series of jobs all at one time. The jobs with similar requirements are batched together and run through the computer as a group. The term originated in the days when users entered programs on punch cards. They would give a batch of these programmed cards to the system operator, who would feed them into the computer. Batch jobs can be stored up during working hours and then executed during the evening or whenever the computer is idle. Batch processing is particularly useful for operations that require the computer or a peripheral device for an extended period of time. Once a batch job begins, it continues until it is done or until an error occurs. Note that batch processing implies that there is no interaction with the user while the program is being executed.
For example: The credit card companies process the billing system. The customer does not receive a bill for each separate credit card purchase but one monthly bill for all of that month’s purchases. The bill is created through batch processing, where all of the data are collected and held until the bill is processed as a batch at the end of the billing cycle.

Features
1)    In this system data is collected for defind period of time and processed in batches.
2)    It is a simplest processing method.
3)    Information of master file is up to date only up to last execution.
4)    Magnetic tapes as well as magnetic disks are used, output reports are printed in detail.



TIME SHARINGOPERATING SYSTEM
                   Time-sharing is an approach to interactive computing in which a single computer is used to provide simultaneous interactive general-purpose computing to multiple users by sharing processor time. This is done by providing a separate terminal to each user. Each terminal is connected to main computer system. CPU time one by one. This short period of time is called time slice. The user feels that he is having his own computer. In time sharing system hundreds of users may be using the system simultaneously. It is not possible to keep the programs of all the users in the memory at the same time. So operating system keeps few programs in the main memory and the rest of the programs stored in the disk.

Advantages
1)    The response time is very less in case of time sharing systems.
2)    The CPU utilization is increased.
3)    The memory management in time sharing system provides for the protection and separation of user programs.
4)    It is cost effective.


REAL TIME OPERATING SYSTEM
When the time requirements on the operation of processor ot the flow of data are very critical, then real time operating systems are used. Real time means a quick response from the computer. In the real time system each process is assigned a priority according to the importance of process. The processor is normally allocated to the highest priority process among those which are ready to execute.

For example:
1)  Air traffic control system
2)  Chemical process control system.
3)  Scientific experiments
4)  Real time simulations
5)  Medical equipment
6)  Automotive applications etc.

Types of real time systems:
1 Hard real time system
2 Soft real time system


ONLINE SYSTEMS
                In online systems, there is direct interaction of the user and the computer and the response time is very less. Each user is provided the direct access to the CPU on time sharing basis. The transactions in the online systems are processed as soon as the data is entered into the system.


For examples:
a)      Railway reservation system
b)      Banking system
c)       Stock prices in the stock market etc.


OFFLINE SYSTEMS
               In offline systems, the transactions are not processed immediately rather the data is collected for some specific period of time and the processing is done after the specific time. The batch processing is the best example of offline system where the jobs are collected and processed after certain time interval.

About rel="canonical"



What is a canonical page?



A canonical page is the preferred version of a set of pages with highly similar content.


Why specify a canonical page?



It's common for a site to have several pages listing the same set of products. For example, one page might display products sorted in alphabetical order, while other pages display the same products listed by price or by rating. For example:

http://www.example.com/product.php?item=swedish-fish&trackingid=1234567&sort=alpha&sessionid=5678asfasdfasfd
http://www.example.com/product.php?item=swedish-fish&trackingid=1234567&sort=price&sessionid=5678asfasdfasfd


If Google knows that these pages have the same content, we may index only one version for our search results. Our algorithms select the page we think best answers the user's query. Now, however, users can specify a canonical page to search engines by adding a element with the attribute rel="canonical" to the  section of the non-canonical version of the page. Adding this link and attribute lets site owners identify sets of identical content and suggest to Google: "Of all these pages with identical content, this page is the most useful. Please prioritize it in search results."


How do I specify a canonical URL?



You can specify a canonical URL in two ways:


  • Add a rel="canonical" link to the  section of the non-canonical version of each HTML page.

    To specify a canonical link to the page http://www.example.com/product.php?item=swedish-fish, create a  element as follows:



    Copy this link into the  section of all non-canonical versions of the page, such as http://www.example.com/product.php?item=swedish-fish&sort=price.


    If you publish content on both http://www.example.com/product.php?item=swedish-fish and https://www.example.com/product.php?item=swedish-fish, you can specify the canonical version of the page. Create the  element:



    Add this link to the  section of https://www.example.com/product.php?item=swedish-fish.


  • Indicate the canonical version of a URL by responding with the Link rel="canonical" HTTP header. Adding rel="canonical" to the headsection of a page is useful for HTML content, but it can't be used for PDFs and otherfile types indexed by Google Web Search. In these cases you can indicate a canonical URL by responding with the Link rel="canonical" HTTP header, like this (note that to use this option, you'll need to be able to configure your server):



    Link: ; rel="canonical"


    Google currently supports these link header elements for Web Search only.




Is rel="canonical" a suggestion or a directive?



This new option lets site owners suggest the version of a page that Google should treat as canonical. Google will take this into account, in conjunction with other signals, when determining which URL sets contain identical content, and calculating the most relevant of these pages to display in search results.


Can the link be relative or absolute?



rel="canonical" can be used with relative or absolute links, but we recommend using absolute links to minimize potential confusion or difficulties. If your document specifies a base link, any relative links will be relative to that base link.


Must the content on a set of pages be similar to the content on the canonical version?



Yes. The rel="canonical" attribute should be used only to specify the preferred version of many pages with identical content (although minor differences, such as sort order, are okay).


For instance, if a site has a set of pages for the same model of dance shoe, each varying only by the color of the shoe pictured, it may make sense to set the page highlighting the most popular color as the canonical version so that Google may be more likely to show that page in search results. However, rel="canonical" would not be appropriate if that same site simply wanted a gel insole page to rank higher than the shoe page.


What happens if rel="canonical" points to a non-existent page? Or if more than one page in a set is specified as the canonical version?



We'll do our best to algorithmically determine an appropriate canonical page, just as we've done in the past.


Can Google follow a chain of rel="canonical" designations?



Yes, to some extent, but to ensure optimal canonicalization, we strongly recommend that you update links to point to a single canonical page.


Can rel="canonical" be used to suggest a canonical URL on a completely different domain?



There are situations where it's not easily possible to set up redirects. This could be the case when you need to migrate to a new domain name using a web server that cannot create server-side redirects. In this case, you can use the rel="canonical" link element to specify the exact URL of the domain preferred for indexing. While therel="canonical" link element is seen as a hint and not an absolute directive, we do try to follow it where possible.






Monday, 29 July 2013

OBJECT ORIENTED PROGRAMMING (OOP)



OBJECT ORIENTED PROGRAMMING (OOP)

It will certainly be moral to say that object oriented programming acts as the seventh heaven for the programmers. Till 1970s, object orientation was just thinking among programmers. But using the object oriented approach in C++ is just incredible. The prospect to accustom programming to objects allows the programmer to design various applications and to reuse the code in a more logical and creative manner. Object- oriented approach reveals a particular way of viewing about problems and tasks in terms of recognizing and describing the behavior of the applicable objects. Smalltalk is a classical example of a pure object-oriented language. C++ incorporates the facilities for both the object-oriented programming and conventional procedural programming. C++ adjoins many enhancements of its own to fresh up the problems that were present in the original C language.

                   Structured programming can be roughly divided into two categories:
 


                      Structured programming is basically dividing a program into smaller modules that are easier to manage. All of what we have covered up to this point is part of procedural programming in this the programmer will divide the program into smaller functions (rather than putting the entire code within one function). Each function would have its own variables and sharing of variables between various functions is also possible. What we will see henceforth is related to object oriented programming (OOP). Large programs were difficult to handle in procedural programming an=d OOP was developed to reduce complexity of software development. In C++, OOP is implemented using classes. The main concepts in OOP are:

Saturday, 27 July 2013

A virus cannot cause any damage to the physical devices connected to the infected computer



VIRUSES
Virus stands for vital information under siege. A virus is a destructive program that is designed to destroy the information stored in computer. It enters the system without the knowledge of the user. It enters through infected floppy or infected program or through network. It makes multiple copies of itself and causes the abnormal functioning in the system. When a virus travels through a network then it spreads to all the computers connected to the network. Virus forms its copies and place them in to the main memory. When a program is being executed by the user the virus attaches its copy to that program.


              A virus cannot cause any damage to the physical devices connected to the infected computer:-
1 It decreases the speed of the computer.
2 It erases the information stored in primary and secondary memory of the system.
3 It displays unusual messages on the screen.
4 Some powerful virus can delete the instruction in the BIOS of the Motherboard.

Types of Viruses
1 Times bound viruses
2 Trojan horses
3 Worms
4 Boot sector viruses.
5 File viruses
6 Macro viruses
7 E-mail viruses