A software bug (or just "bug") is an error, flaw, mistake, failure, fault or "undocumented feature" in a computer program that prevents it from behaving as intended (e. Failure ( fail, phail or flop) in general refers to the state or Condition of not meeting a desirable or intended objective In document ISO/CD 10303-226, a fault is defined as an abnormal condition or defect at the component equipment or sub-system level which may lead to a Failure. Computer programs (also software programs, or just programs) are instructions for a Computer. g. , producing an incorrect result). Most bugs arise from mistakes and errors made by people in either a program's source code or its design, and a few are caused by compilers producing incorrect code. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable The software architecture of a program or computing system is the structure or structures of the system, which comprise software components the externally visible properties A compiler is a Computer program (or set of programs that translates text written in a computer language (the source language) into another A program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy. Reports detailing bugs in a program are commonly known as bug reports, fault reports, problem reports, trouble reports, change requests, and so forth.

Effects

Main article: List of notable software bugs

Bugs can have a wide variety of effects, with varying levels of inconvenience to the user of the program. Many Software bugs are merely annoying or inconvenient but some can have extremely serious consequences - either financially or as a threat to human well-being Some bugs have only a subtle effect on the program's functionality, and may thus lie undetected for a long time. More serious bugs may cause the program to crash or freeze leading to a denial of service. A crash in Computing is a condition where a program (either an application or part of the Operating system) stops performing its expected function and also This article is about the computer malfunction called hanging. Others qualify as security bugs and might for example enable a malicious user to bypass access controls in order to obtain unauthorized privileges. A security bug is a Software bug that benefits someone other than intended beneficiaries in the intended ways A black hat is the Villain or bad guy, especially in a western movie in which such a character would wear a black Hat in contrast to the Access control is the ability to permit or deny the use of a particular resource by a particular entity

The results of bugs may be extremely serious. A bug in the code controlling the Therac-25 radiation therapy machine was directly responsible for some patient deaths in the 1980s. The Therac-25 was a Radiation therapy Machine produced by Atomic Energy of Canada Limited (AECL and CGR MeV of France after the Radiation therapy (or radiotherapy) is the medical use of Ionizing radiation as part of Cancer treatment to control Malignant In 1996, the European Space Agency's US$1 billion prototype Ariane 5 rocket was destroyed less than a minute after launch, due to a bug in the on-board guidance computer program. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Ariane 5 is a European Expendable launch In June 1994, a Royal Air Force Chinook crashed into the Mull of Kintyre, killing 29. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout This was initially dismissed as pilot error, but an investigation by Computer Weekly uncovered sufficient evidence to convince a House of Lords inquiry that it may have been caused by a software bug in the aircraft's engine control computer. ComputerWeekly is a weekly magazine for IT professionals which has been published by Reed Business Information for over 40 years The House of Lords is the second house of the Parliament of the United Kingdom and is also commonly referred to as "the Lords" A FADEC (Full Authority Digital Engine Control is a system consisting of a Digital Computer, called an Electronic Engine Control (EEC or Electronic Control ^[1]

Etymology

The concept that software might contain errors dates back to 1842 in Ada Byron's notes on the analytical engine in which she speaks of the difficulty of preparing program 'cards' for Charles Babbage's Analytical engine:

Usage of the term "bug" to describe inexplicable defects has been a part of engineering jargon for many decades and predates computers and computer software; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, Thomas Edison wrote the following words in a letter to an associate in 1878:

Problems with radar electronics during World War II were referred to as bugs (or glitches), and there is additional evidence that the usage dates back much earlier.

Photo of what is possibly the first real bug found in a computer.

The invention of the term is often erroneously attributed to Grace Hopper, who publicized the cause of a malfunction in an early electromechanical computer^[3] . Rear Admiral Grace Murray Hopper ( December 9 1906 – January 1 1992) was an American Computer scientist and United A typical version of the story is given by this quote:

Hopper was not actually the one who found the insect, as she readily acknowledged. And the date was September 9, but in 1947, not 1945. Events 1000 - Battle of Svolder, Viking Age. 1379 - Treaty of Neuberg, splitting the Austrian Year 1947 ( MCMXLVII) was a Common year starting on Wednesday (link will display full 1947 calendar of the Gregorian calendar. ^[5][6] The operators who did find it (including William "Bill" Burke, later of the Naval Weapons Laboratory, Dahlgren Va. ^[7]), were familiar with the engineering term and, amused, kept the insect with the notation "First actual case of bug being found. " Hopper loved to recount the story. ^[8]

While it is certain that the Mark II operators did not coin the term "bug", it has been suggested that they did coin the related term, "debug". The Harvard Mark II was an electromechanical computer built at Harvard University under the direction of Howard Aiken and was finished in 1947 Even this is unlikely, since the Oxford English Dictionary entry for "debug" contains a use of "debugging" in the context of airplane engines in 1945 (see the debugging article for more). The Oxford English Dictionary ( OED) published by the Oxford University Press (OUP is a comprehensive Dictionary of the English

Prevention

Bugs are a consequence of the nature of human factors in the programming task. See also The Human Factor (disambiguation. Human factors is a term that covers The science of understanding the properties They arise from oversights made by computer programmers during design, coding and data entry. A programmer is someone who writes Computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist For example: In creating a relatively simple program to sort a list of words into alphabetical order, one's design might fail to consider what should happen when a word contains a hyphen. A hyphen ( -) is a Punctuation mark It is used for both Words to join and to separate Syllables It is often confused with the dashes Perhaps, when converting the abstract design into the chosen programming language, one might inadvertently create an off-by-one error and fail to sort the last word in the list. An off-by-one error (OBOE is a logical error involving the discrete equivalent of a Boundary condition. Finally, when typing the resulting program into the computer, one might accidentally type a '<' where a '>' was intended, perhaps resulting in the words being sorted into reverse alphabetical order. More complex bugs can arise from unintended interactions between different parts of a computer program. This frequently occurs because computer programs can be complex - millions of lines long in some cases - often having been programmed by many people over a great length of time, so that programmers are unable to mentally track every possible way in which parts can interact. Another category of bug called a race condition comes about either when a process is running in more than one thread or two or more processes run simultaneously, and the exact order of execution of the critical sequences of code have not been properly synchronized. A race condition or race hazard is a flaw in a System or process whereby the output and/or result of the process is unexpectedly and critically dependent A thread in Computer science is short for a thread of execution.

The software industry has put much effort into finding methods for preventing programmers from inadvertently introducing bugs while writing software. ^[9][10] These include:

Programming style

While typos in the program code most likely are caught by the compiler, a bug usually appears when the programmer makes a logic error. Various innovations in programming style and defensive programming are designed to make these bugs less likely, or easier to spot. Programming style refers to a set of rules or guidelines used when writing the Source code for a Computer program. Defensive programming is a form of Defensive design intended to ensure the continuing function of a piece of Software in spite of unforeseeable usage of said software

Programming techniques

Bugs often create inconsistencies in the internal data of a running program. Programs can be written to check the consistency of their own internal data while running. If an inconsistency is encountered, the program can immediately halt, so that the bug can be located and fixed. Alternatively, the program can simply inform the user, attempt to correct the inconsistency, and continue running.

Development methodologies

There are several schemes for managing programmer activity, so that fewer bugs are produced. Many of these fall under the discipline of software engineering (which addresses software design issues as well. Software engineering is the application of a systematic disciplined quantifiable approach to the development operation and maintenance of Software. ) For example, formal program specifications are used to state the exact behavior of programs, so that design bugs can be eliminated. A functional specification (also functional spec, specs, functional specifications document (FSD, or Program specification) in Software

Programming language support

Programming languages often include features which help programmers deal with bugs, such as exception handling. A programming language is an Artificial language that can be used to write programs which control the behavior of a machine particularly a Computer. Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of a condition that changes the normal flow of execution In addition, many recently-invented languages have deliberately excluded features which can easily lead to bugs. For example, the Java programming language does not support pointer arithmetic.

Debugging

The typical bug history (GNU Classpath project data). GNU Classpath is a project aiming to create a Free software implementation of the standard class library for the Java programming language. A bug, submitted by the user, is unconfirmed. A reproduced bug is a confirmed bug. The confirmed bugs are later fixed. Bugs, belonging to other categories (unreproducible, will not be fixed, etc) are usually in the minority

Main article: Debugging

Finding and fixing bugs, or "debugging", has always been a major part of computer programming. Maurice Wilkes, an early computing pioneer, described his realization in the late 1940s that much of the rest of his life would be spent finding mistakes in his own programs. The 1940s decade ran from 1940 to 1949 Events and trends The 1940s was a period between the radical 1930s and the conservative 1950s which also leads the period to be As computer programs grow more complex, bugs become more common and difficult to fix. Often programmers spend more time and effort finding and fixing bugs than writing new code.

Usually, the most difficult part of debugging is locating the erroneous part of the source code. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable Once the mistake is found, correcting it is usually easy. Programs known as debuggers exist to help programmers locate bugs. A debugger is a Computer program that is used to test and Debug other programs However, even with the aid of a debugger, locating bugs is something of an art. It is not uncommon for a bug in one section of a program to cause failures in a completely different section, thus making it especially difficult to track (for example, an error in a graphic rendering routine causing a file I/O routine to fail); this is most commonly caused by errors that lead to the corruption of program instructions or variables in memory. Rendering is the process of generating an image from a model, by means of computer programs In Computing, input/output, or I/O, refers to the communication between an Information processing system (such as a Computer) and the outside

Typically, the first step in locating a bug is finding a way to reproduce it easily. Once the bug is reproduced, the programmer can use a debugger or some other tool to monitor the execution of the program in the faulty region, and find the point at which the program went astray. Sometimes, a bug is not a single flawed instruction, but represents an error of thinking or planning on the part of the programmer. Such logic errors require a section of the program to be overhauled or rewritten. In Computer programming, a logic error (sometimes called a semantic error) is a bug in a program that causes it to operate incorrectly but not to

It is not always easy to reproduce bugs. Some bugs are triggered by inputs to the program which may be difficult for the programmer to re-create. One cause of the Therac-25 radiation machine deaths was a bug that occurred only when the machine operator very rapidly entered a treatment plan; it took days of practice to become able to do this, so the bug did not manifest in testing or when the manufacturer attempted to duplicate it. The Therac-25 was a Radiation therapy Machine produced by Atomic Energy of Canada Limited (AECL and CGR MeV of France after the Other bugs may disappear when the program is run with a debugger; these are heisenbugs (humorously named after the Heisenberg uncertainty principle. Unusual software bugs are a class of Software bugs that are considered exceptionally difficult to understand and repair In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain )

Debugging is still a tedious task requiring considerable manpower. Since the 1990s, particularly following the Ariane 5 Flight 501 disaster, there has been a renewed interest in the development of effective automated aids to debugging. Flight 501, which took place on June 4, 1996, was the first and unsuccessful test flight of the European Ariane 5 Expendable launch system. For instance, methods of static code analysis by abstract interpretation have already made significant achievements, while still remaining much of a work in progress. Static code analysis is the analysis of computer Software that is performed without actually executing programs built from that software (analysis performed on executing In Computer science, abstract interpretation is a theory of sound approximation of the Semantics of computer programs based on Monotonic functions

Bug management

It is common practice for software to be released with known bugs that are considered non-critical. While software products contain an unknown number of unknown bugs when shipped, measurements during the testing may provide a statistically reliable estimate of the number of likely bugs remaining. Most big software projects maintain a list of "known bugs". This list inform users about bugs that are not fixed in the current release, or not fixed at all, and often a workaround is offered additionally. A workaround is a bypass of a recognized problem in a system A workaround is typically a temporary fix that implies that a genuine solution to the problem is needed

There are various reasons for such a list:

• The developers often don't have time to fix all non-severe bugs.
• The bug could be fixed in a new version or patch that is not yet released.
• The changes to the code required to fix the bug would be large, and would bring with them the chance of introducing other bugs into the system.

Given the above, it is often considered impossible to write completely bug-free software of any real complexity. So bugs are categorized by severity, and low-severity non-critical bugs are tolerated, as they do not impact the proper operation of the system, for the majority of users. NASA's SATC managed to reduce number of errors to fewer than 0. The Software Assurance Technology Center (SATC is a NASA department founded in 1992 as part of their Systems Reliability and Safety Office at GSFC. 1 per 1000 lines of code (SLOC) but this was not felt to be feasible for any real world projects.

One school of thought, popularized by Eric S. Raymond as Linus's Law in his essay The Cathedral and the Bazaar, holds that popular open-source software holds a better chance of having few or no bugs than other software, because "given enough eyeballs, all bugs are shallow". Eric Steven Raymond (born December 4 1957 often referred to as ESR, is a Computer programmer, author and Open source software advocate Linus's Law can refer to two different notions both named after Linus Torvalds. The Cathedral and the Bazaar (abbreviated CatB) is an essay by Eric S Open source software (OSS began as a marketing campaign for Free software. ^[11] This assertion has been disputed, however: computer security specialist Elias Levy wrote that "it is easy to hide vulnerabilities in complex, little understood and undocumented source code," because, "even if people are reviewing the code, that doesn't mean they're qualified to do so. Elias Levy (also known as Aleph One) was the moderator of the Full disclosure vulnerability mailing list Bugtraq from May 14 1996 "^[12]

Security vulnerabilities

Malicious software may attempt to exploit known vulnerabilities in a system - which may or may not be bugs. Malware, a Portmanteau word from the words '''mal'''icious and soft'''ware''', is software designed to infiltrate or damage a computer system without Viruses are not bugs in themselves - they are typically programs that are doing precisely what they were designed to do. However, viruses are occasionally referred to as such in the popular press.

Common types of computer bugs

• Division by zero
• NULL pointer dereference
• Infinite loops
• Arithmetic overflow or underflow
• Using an uninitialized variable
• Accessing memory not owned (Access violation)
• Memory leak or Handle leak
• Buffer overflow
• Deadlock
• Off by one error
• Race condition
• Loss of precision in type conversion
• Assignment instead of equality test

Bugs in popular culture

• In the 1968 novel 2001: A Space Odyssey (and the corresponding film), a spaceship's onboard computer, HAL 9000, is programmed with two conflicting objectives: to fully disclose all its information, and to keep the true purpose of the flight secret from the crew. In An infinite loop is a sequence of instructions in a computer program which loops endlessly either due to the loop having no terminating condition or having one that can The term arithmetic overflow or simply overflow has the following meanings Arithmetic underflow (or "floating point underflow" "floating underflow" In Computing, an uninitialized variable is a Variable that is declared but is not set to a definite known value before it is used A segmentation fault (often shortened to segfault) is a particular error condition that can occur during the operation of Computer software. In Computer science, a memory leak is a particular type of unintentional memory consumption by a Computer program where the program fails to release memory A handle leak is a type of Software bug that occurs when a Computer program asks for a handle to a resource but does not free the handle when it is no longer In Computer security and programming, a buffer overflow, or buffer overrun, is an anomalous condition where a process attempts to A deadlock is a situation wherein two or more competing actions are waiting for the other to finish and thus neither ever does An off-by-one error (OBOE is a logical error involving the discrete equivalent of a Boundary condition. A race condition or race hazard is a flaw in a System or process whereby the output and/or result of the process is unexpectedly and critically dependent In Computer science, type conversion or typecasting refers to changing an entity of one Data type into another In Computer science a relational operator is a Programming language construct or operator that tests some kind of relation between two entities For other uses see 2001 A Space Odyssey. 2001 A Space Odyssey ( 1968) is a Science fiction Novel 2001 A Space Odyssey is a 1968 Science fiction film directed by Stanley Kubrick, written by Kubrick and Arthur C HAL 9000 ( Heuristically programmed ALgorithmic Computer is a fictional Computer in Arthur C This conflict causes HAL to eventually try to kill all the crew members (since, if there were no crew, there would be no contradiction).
• In the 1984 song 99 Red Balloons (though not in the original German version), "bugs in the software" lead to a computer mistaking a group of balloons for a nuclear missile and starting a nuclear war. " 99 Luftballons " is a Cold War -era Protest song by the German band Nena. Nuclear weapons delivery is the technology and systems used to place a Nuclear weapon at the position of Detonation, on or near its intended target
• The 2004 novel The Bug, by Ellen Ullman, is about a programmer's attempt to find an elusive bug in a database application. Ellen Ullman is an American Computer Programmer and Author. She has written Novels as well as articles for various publications

See also

• Glitch
• ISO 9126, which classifies a bug as either a defect or a nonconformity
• Workaround
• Bug tracking system
• Bit rot
• Anti-pattern
• Unusual software bugs (schroedinbug, heisenbug, Bohr bug, and mandelbug)

Notes

1. ^ The Chinook Helicopter Disaster
2. ^ Edison to Puskas, 13 November 1878, Edison papers, Edison National Laboratory, U. A glitch is a short-lived Fault in a system The term is particularly common in the Computing and Electronics industries and in Circuit bending ISO 9126 is an International standard for the Evaluation of Software quality. A workaround is a bypass of a recognized problem in a system A workaround is typically a temporary fix that implies that a genuine solution to the problem is needed Bug report redirects here To report bugs with the MediaWiki software that powers Wikipedia see WikipediaBug reports. Bit rot, or bit decay, is a colloquial Computing term used either to describe gradual decay of storage media or to facetiously describe the spontaneous degradation In Software engineering, an anti-pattern (or antipattern) is a Design pattern that appears obvious but is ineffective or far from optimal in practice Unusual software bugs are a class of Software bugs that are considered exceptionally difficult to understand and repair Events 1002 - English king Ethelred orders the killing of all Danes in England, known today as the St Year 1878 ( MDCCCLXXVIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common S. National Park Service, West Orange, N. J. , cited in Thomas P. Hughes, American Genesis: A History of the American Genius for Invention, Penguin Books, 1989, ISBN 0-14-009741-4, on page 75.
3. ^ {{{author}}}, FCAT NRT Test, Harcourt, 03/18/2008. The Florida Comprehensive Assessment Test, or the FCAT, is the standardized test used in the primary and secondary public schools of Florida.
4. ^ Danis, Sharron Ann: "Rear Admiral Grace Murray Hopper"[1]
5. ^ Definition of bug
6. ^ Log Book With Computer Bug
7. ^ IEEE Annals of the History of Computing, Vol 22 Issue 1, 2000
8. ^ First Computer Bug
9. ^ Huizinga, Dorota; Kolawa, Adam (2007). Automated Defect Prevention: Best Practices in Software Management. Wiley-IEEE Computer Society Press, 426. ISBN 0470042125.  
10. ^ McDonald, Marc; Musson, Robert; Smith, Ross (2007). The Practical Guide to Defect Prevention. Microsoft Press, 480. ISBN 0735622531.  
11. ^ "Release Early, Release Often", Eric S. Raymond, The Cathedral and the Bazaar
12. ^ "Wide Open Source", Elias Levy, SecurityFocus, April 17, 2000

External links

• Collection of Software Bugs (Thomas Huckle, TU München)
• Computer-Related Incidents with Commercial Aircraft (Peter B. Eric Steven Raymond (born December 4 1957 often referred to as ESR, is a Computer programmer, author and Open source software advocate The Cathedral and the Bazaar (abbreviated CatB) is an essay by Eric S Elias Levy (also known as Aleph One) was the moderator of the Full disclosure vulnerability mailing list Bugtraq from May 14 1996 Ladkin et al. , Universität Bielefeld)
• An Investigation of the Therac-25 Accidents (Nancy Leveson, University of Washington and Clark S. Prof Nancy G Leveson is a leading American expert in system and Software safety. Turner, University of California at Irvine)
• Fatal Dose: Radiation Deaths linked to AECL Computer Errors (Barbara Wade Rose, Canadian Coalition for Nuclear Responsibility)
• Software Horror Stories (Nachum Dershowitz)
• Software Does Not Fail (Paul Niquette]
• Picture of the "first computer bug" The error of this term is elaborated above. (Naval Historical Center)
• Page from 1947 log book with "first actual case of bug being found" (moth) (National Museum of American History)
• The First Computer Bug! An email from 1981 about Adm. The National Museum of American History collects preserves and displays American heritage in the areas of social political cultural scientific and military history Hopper's bug
• How to Report Bugs Effectively (Simon G. Tatham)
• Rates of Design Failure
• Bug Tracking Basics: A beginner’s guide to reporting and tracking defects (Mitch Allen)
• History's Worst Software Bugs
• Bug Isolation Project - This project is to track bugs of popular open source software. Simon Tatham (born May 3, 1977) is an English Programmer known primarily for creating and maintaining PuTTY, a Free software implementation (Packages for Fedora available)