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Sentinel Value
In computer programming, a sentinel value (also referred to as a flag value, trip value, rogue value, signal value, or dummy data) is a special value in the context of an algorithm which uses its presence as a condition of termination, typically in a loop or recursive algorithm. The sentinel value is a form of in-band data that makes it possible to detect the end of the data when no out-of-band data (such as an explicit size indication) is provided. The value should be selected in such a way that it is guaranteed to be distinct from all legal data values since otherwise, the presence of such values would prematurely signal the end of the data (the semipredicate problem). A sentinel value is sometimes known as an " Elephant in Cairo," due to a joke where this is used as a physical sentinel. In safe languages, most sentinel values could be replaced with option types, which enforce explicit handling of the exceptional case. Examples Some examples of common sentinel values and their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms (usually in a chosen programming language, commonly referred to as coding). The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an operating system) on a computer, often for solving a given problem. Proficient programming thus usually requires expertise in several different subjects, including knowledge of the application domain, specialized algorit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of technical limitations of computer systems at the time it was invented, ASCII has just 128 code points, of which only 95 are , which severely limited its scope. All modern computer systems instead use Unicode, which has millions of code points, but the first 128 of these are the same as the ASCII set. The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding. ASCII is one of the IEEE milestones. Overview ASCII was developed from telegraph code. Its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. Work on the ASCII standard began in May 1961, with the first meeting of the American Standards Association's (ASA) (now the American National Standards I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Formatting And Storage Bugs
In computer science, time formatting and storage bugs are a class of software bugs that may cause time and date calculation or display to be improperly handled. These are most commonly manifestations of arithmetic overflow, but can also be the result of other issues. The most well-known consequence of bugs of this type is the Y2K problem, but many other milestone dates or times exist that have caused or will cause problems depending on various programming deficiencies. Year 1975 On 4 January 1975, the 12-bit field that had been used for dates in the DECsystem-10 operating systems overflowed. There were numerous problems and crashes related to this bug while an alternative format was developed. Year 1978 The Digital Equipment Corporation OS/8 operating system for the PDP-8 computer used only three bits for the year, representing the years 1970 to 1977. This was recognized when the later COS-310 operating system was developed, and dates were recorded differently. Year 198 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Null Object Pattern
In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (''null'') behavior. The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" and later in the ''Pattern Languages of Program Design'' book series as "Null Object" . Motivation In most object-oriented languages, such as Java or C#, references may be null. These references need to be checked to ensure they are not null before invoking any methods, because methods typically cannot be invoked on null references. The Objective-C language takes another approach to this problem and does nothing when sending a message to nil; if a return value is expected, nil (for objects), 0 (for numeric values), NO (for BOOL values), or a struct (for struct types) with all its members initialised to null/0/NO/zero-initialised struct is returned. Description Instead of using a null referenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magic String
In computer programming, a magic string is an input that a programmer believes will never come externally and which activates otherwise hidden functionality. A user of this program would likely provide input that gives an expected response in most situations. However, if the user does in fact innocently provide the pre-defined input, invoking the internal functionality, the program response is often quite unexpected to the user (thus appearing "magical"). Background Typically, the implementation of magic strings is due to time constraints. A developer must find a fast solution instead of delving more deeply into a problem and finding a better solution. For example, when testing a program that takes a user's personal details and verifies their credit card number, a developer may decide to add a magic string shortcut whereby entering the unlikely input of "***" as a credit card number would cause the program to automatically proceed as if the card were valid, without spending ti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magic Number (programming)
In computer programming, a magic number is any of the following: * A unique value with unexplained meaning or multiple occurrences which could (preferably) be replaced with a named constant * A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures * A distinctive unique value that is unlikely to be mistaken for other meanings (e.g., Globally Unique Identifiers) Unnamed numerical constants The term ''magic number'' or ''magic constant'' refers to the anti-pattern of using numbers directly in source code. This has been referred to as breaking one of the oldest rules of programming, dating back to the COBOL, FORTRAN and PL/1 manuals of the 1960s. The use of unnamed magic numbers in code obscures the developers' intent in choosing that number, increases opportunities for subtle errors (e.g. is every digit correct in 3.14159265358979323846 and is this equal to 3.14159?) and makes it more difficult for the program to be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semipredicate Problem
In computer programming, a semipredicate problem occurs when a subroutine intended to return a useful value can fail, but the signalling of failure uses an otherwise valid return value. The problem is that the caller of the subroutine cannot tell what the result means in this case. Example The division operation yields a real number, but fails when the divisor is zero. If we were to write a function that performs division, we might choose to return 0 on this invalid input. However, if the dividend is 0, the result is 0 too. This means there is no number we can return to uniquely signal attempted division by zero, since all real numbers are in the range of division. Practical implications Early programmers dealt with potentially exceptional cases, as in the case of division, using a convention that required the calling routine to check the validity of the inputs before calling the division function. This had two problems. First, it greatly encumbers all code that performs div ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sentinel Node
In computer programming, a sentinel node is a specifically designated node used with linked lists and trees as a traversal path terminator. This type of node does not hold or reference any data managed by the data structure. Benefits Sentinels are used as an alternative over using NULL as the path terminator in order to get one or more of the following benefits: * Marginally increased speed of operations * Increased data structure robustness (arguably) Drawbacks * Marginally increased algorithmic complexity and code size. * If the data structure is accessed concurrently (which means that all nodes being accessed have to be protected at least for “read-only”), for a sentinel-based implementation the sentinel node has to be protected for “read-write” by a mutex. This extra mutex in quite a few use scenarios can cause severe performance degradation. One way to avoid it is to protect the list structure as a whole for “read-write”, whereas in the version with NULL i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canary Value
Canary originally referred to the island of Gran Canaria on the west coast of Africa, and the group of surrounding islands (the Canary Islands). It may also refer to: Animals Birds * Canaries, birds in the genera '' Serinus'' and '' Crithagra'' including, among others: ** Atlantic canary (''Serinus canaria''), a small wild bird *** Domestic canary, ''Serinus canaria domestica'', a small pet or aviary bird, also responsible for the "canary yellow" color term ** Yellow canary (''Serinus flaviventris''), a small bird Fish * Canary damsel (''Similiparma lurida''), fish of the family Pomacentridae, found in the eastern Atlantic Ocean * Canary moray (''Gymnothorax bacalladoi''), an eel of the family Muraenidae * Canary rockfish (''Sebastes pinniger''), of the family Sebastidae, found in the northeast Pacific Ocean People * Canary Burton (born 1942), American keyboardist, composer and writer * Canary Conn (born 1949), American entertainer and author * Bill Canary (fl. 1994), Repub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inner Loop , United States
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Inner loop may refer to: * Inner loop in computer programs * Inner Loop (Phoenix), a section of Interstate 10 in downtown Phoenix, Arizona, United States * Inner Loop (Rochester), an expressway around downtown Rochester, New York, United States * Inner Loop (Washington, D.C.), a previously proposed freeway loop in Washington, D.C., United States * Inner–outer directions, where "inner loop" is used to describe the clockwise traveling lanes of a roadway **This usage of "inner loop" is commonly applied to the clockwise roadway of Interstate 495 (Capital Beltway) *Interstate 610 (Texas), the innermost highway loop around the central area of Houston, Texas Houston (; ) is the most populous city in Texas, the most populous city in the Southern United States, the fourth-most populous city in the United States, and the sixth-most populous city in North America, with a population of 2,304,580 i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List (abstract Data Type)
In computer science, a list or sequence is an abstract data type that represents a finite number of ordered values, where the same value may occur more than once. An instance of a list is a computer representation of the mathematical concept of a tuple or finite sequence; the (potentially) infinite analog of a list is a stream. Lists are a basic example of containers, as they contain other values. If the same value occurs multiple times, each occurrence is considered a distinct item. The name list is also used for several concrete data structures that can be used to implement abstract lists, especially linked lists and arrays. In some contexts, such as in Lisp programming, the term list may refer specifically to a linked list rather than an array. In class-based programming, lists are usually provided as instances of subclasses of a generic "list" class, and traversed via separate iterators. Many programming languages provide support for list data types, and have spec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Italics
In typography, italic type is a cursive font based on a stylised form of calligraphic handwriting. Owing to the influence from calligraphy, italics normally slant slightly to the right. Italics are a way to emphasise key points in a printed text, to identify many types of creative works, to cite foreign words or phrases, or, when quoting a speaker, a way to show which words they stressed. One manual of English usage described italics as "the print equivalent of underlining"; in other words, underscore in a manuscript directs a typesetter to use italic. The name comes from the fact that calligraphy-inspired typefaces were first designed in Italy, to replace documents traditionally written in a handwriting style called chancery hand. Aldus Manutius and Ludovico Arrighi (both between the 15th and 16th centuries) were the main type designers involved in this process at the time. Along with blackletter and Roman type, it served as one of the major typefaces in the history of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
