Caret
Caret (
/ˈkærət/) usually refers to the spacing symbol ^ in ASCII (at code point 5Ehex) and other character sets. In Unicode, however, the corresponding character is U+005E ^ circumflex accent (HTML: ^), whereas the Unicode character named caret is actually a similar but lowered symbol: U+2038 ‸ caret (HTML: ‸).
A caret can also be called a wedge, up-arrow, hat, control character, or chevron.[1]
In graphical user interface terminology, caret sometimes refers to a text insertion point indicator, often a blinking vertical bar. In this context, it may be used interchangeably with the word cursor.
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[edit] Origins
As the variation in naming shows, the origins of the character are twofold. The caret was originally used, and continues to be, in handwritten form as a proofreading mark to indicate where a punctuation mark, word, or phrase should be inserted in a document.[2] The term comes from the Latin caret, "it lacks", from 'carēre', to lack; to be separated from; to be free from. The caret symbol is written below the line of text for a line-level punctuation mark such as a comma, or above for a higher character such as an apostrophe; the material to be inserted may be placed inside the caret, in the margin, or above the line.
A raised variant of the character can be found on some typewriters, where it is used to denote a circumflex in some languages, such as French and Portuguese. It is typically a dead key, which does not cause the carriage to advance and thus allows the following letter to strike the same spot (below the circumflex) on the paper.
In the original 1963 version of the ASCII standard, code point 5Ehex was reserved for an up-arrow (↑). However, the 1965 ECMA-6 standard replaced the up-arrow with a circumflex ( ˆ ), which was applicable as a diacritic as well, and two years later, the second revision of ASCII followed suit.[3] As the early mainframes and minicomputers largely used teleprinters as output devices, it was possible to print the circumflex above a letter when needed. With the proliferation of monitors, however, this became insufficient, and precomposed characters, with the diacritic included, were instead introduced into appended character sets, such as Latin-1. The original circumflex character was left for other purposes, and as it did not need to fit above a letter anymore, it was made larger in appearance.[4]
[edit] Other uses
In mathematics, the caret can signify exponentiation (3^5 for 35), where the usual superscript is not readily usable (as on some graphing calculators). The caret is also now used to indicate a superscript in TeX typesetting. As Isaac Asimov described it in his 1974 "Skewered" essay (on Skewes' number), "I make the exponent a figure of normal size and it is as though it is being held up by a lever, and its added weight when its size grows bends the lever down."[5] The use of the caret for exponentiation can be traced back to ALGOL 60, which expressed the exponentiation operator as an upward-pointing arrow, intended to evoke the superscript notation common in mathematics. The upward-pointing arrow is now used as a form of iterated exponentiation in Knuth's up-arrow notation.
The caret has many uses in programming languages. It can signify exponentiation, the bitwise XOR operator, string concatenation, and control characters in caret notation, among other uses. In regular expressions, the caret is used to mark the beginning of a string, or the beginning of a line within that string (depending on the regular expression dialect and specified options); if it begins a character class, it indicates that the inverse of the class is to be matched. Pascal uses the caret when dereferencing pointers.
The command-line interpreter, cmd.exe, of Windows family of operating systems uses the caret to escape reserved characters.
In C++/CLI the only type of pointer is C++ pointer, and the .NET reference types are accessed through a "handle", with the new syntax ClassName^ instead of ClassName*. This new construct is especially helpful when managed and standard C++ code is mixed; it clarifies which objects are under .NET automatic garbage collection and which objects the programmer must remember to explicitly destroy. In development for Apple's Mac OS X and iOS, carets are used to create blocks, and to denote block types.
In logic, an enlarged caret called a wedge symbol is used as a propositional operator to symbolize logical conjunction, otherwise known as an and (e.g., p
q).
In Italian, the caret is sometimes used in a similar manner to the ordinal indicator, most noticeably on tickets from Trenitalia, the primary operator of trains within Italy, and Rome's ATAC public transit system. On Trenitalia tickets, the travel class is often written as 1^ or 2^, meaning first class or second class respectively. This is due to the lack of the ordinal indicator (-o) used in Italian in the ASCII set.
In music notation, a caret placed above a note indicates marcato, a special form of emphasis or accent. In music for string instruments, a narrow inverted caret indicates that a note should be performed up-bow.
In music theory and musicology, a caret placed above a numeral is used to make reference to a particular scale degree.
In social network services such as Twitter, a caret placed before a word is used to tag that word as an individual's signature within a group account. This differentiates an individual's contribution from a group-authored contribution. Alternatively, a caret placed beneath the post of one user, by another user indicates that they agree with what was stated in the previous post.
[edit] See also
[edit] Notes
- ^ "Caret". TheFreeDictionary.com. Farlex. http://encyclopedia2.thefreedictionary.com/caret. Retrieved 20 July 2010.
- ^ MLA Handbook for Writers of Research Papers (7 ed.). New York: Modern Language Association. 2009. p. 121. ISBN 9781603290241.
- ^ Tom Jennings. "ASCII: American Standard Code for Information Infiltration". http://www.wps.com/projects/codes/index.html#UP. Retrieved 14 September 2010.
- ^ Jukka K. Korpela (18 January 2010). "Kirjainten tarinoita" (in Finnish) (PDF). pp. 132–133. http://www.cs.tut.fi/~jkorpela/kirjaimet/tarinoita.pdf. Retrieved 14 September 2010.
- ^ Asimov, Isaac (1974), "Skewered", Of Matters Great and Small, Doubleday, ISBN 978-0385022255
[edit] References
- Weisstein, Eric W., "Caret" from MathWorld.
