String (computer science): Difference between revisions

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Revision as of 18:55, 3 July 2024

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{{Short description|Sequence of characters, data type}}

[[File:String example.png|alt=Diagram of String data in computing. Shows the word "example" with each letter in a separate box. The word "String" is above, referring to the entire sentence. The label "Character" is below and points to an individual box.|thumb|Strings are typically made up of [[character (computing)|characters]], and are often used to store human-readable data, such as words or sentences.]]

In [[computer programming]], a '''string''' is traditionally a [[sequence]] of [[character (computing)|characters]], either as a [[literal (computer programming)|literal constant]] or as some kind of [[Variable (computer science)|variable]]. The latter may allow its elements to be [[Immutable object|mutated]] and the length changed, or it may be fixed (after creation). A string is generally considered as a [[data type]] and is often implemented as an [[array data structure]] of bytes[[byte]]s (or words[[word (computer architecture)|word]]s) that stores a sequence of elements, typically characters, using some [[character encoding]]. ''String'' may also denote more general [[Array data type|arrays]] or other sequence (or [[List (abstract data type)|list]]) data types and structures.

Depending on the programming language and precise data type used, a [[variable (programming)|variable]] declared to be a string may either cause storage in memory to be statically allocated for a predetermined maximum length or employ [[dynamic allocation]] to allow it to hold a variable number of elements.

When a string appears literally in [[source code]], it is known as a [[string literal]] or an anonymous string.<ref>{{cite web|url=http://www.acsu.buffalo.edu/~fineberg/mfc158/week10lecture.htm|title=Introduction To Java – MFC 158 G|quote=String literals (or constants) are called ‘anonymous strings’|url-status=live|archive-url=https://web.archive.org/web/20160303233357/http://www.acsu.buffalo.edu/~fineberg/mfc158/week10lecture.htm|archive-date=2016-03-03}}</ref>

In [[formal languageslanguage]]s, which are used in [[mathematical logic]] and [[theoretical computer science]], a string is a finite sequence of symbols[[symbol (formal)|symbol]]s that are chosen from a [[set (mathematics)|set]] called an [[alphabet (computer science)|alphabet]].

== Purpose ==

A primary purpose of strings is to store human-readable text, like words and sentences. Strings are used to communicate information from a computer program to the user of the program.<ref>{{cite web |url=https://users.cs.utah.edu/~germain/PPS/Topics/strings.html |website=University of Utah, Kahlert School of Computing |title=Strings
|first=H. James |last=de St. Germain }}</ref> A program may also accept string input from its user. Further, strings may store data expressed as characters yet not intended for human reading.

Example strings and their purposes:

* A message like "<code>file upload complete</code>" is a string that software shows to [[end usersuser]]s. In the program's [[source code]], this message would likely appear as a [[string literal]].

* User-entered text, like "<code>I got a new job today</code>" as a status update on a [[social media]] service. Instead of a string literal, the software would likely store this string in a [[database]].

* Alphabetical data, like "<code>AGATGCCGT</code>" representing nucleic acid sequences of [[DNA]].<ref>{{cite web |url=https://plant-breeding-genomics.extension.org/dna-as-a-biochemical-entity-and-data-string/ |title=DNA as a Biochemical Entity and Data String |date=November 14, 2019 |first1=David M. |last1=Francis |first2=Heather L. |last2=Merk }}</ref>

* Computer settings or parameters, like "<code>?action=edit</code>" as a URL [[query string]]. Often these are intended to be somewhat human-readable, though their primary purpose is to communicate to computers.

The term string may also designate a sequence of data or computer records other than characters {{mdash}} like a "string of bits[[bit]]s" {{mdash}} but when used without qualification it refers to strings of characters.<ref name=Burchfield1986 />

==History==

Use of the word "string" to mean any items arranged in a line, series or succession dates back centuries.<ref>{{cite encyclopedia |encyclopedia=The Oxford English Dictionary |volume=X |publisher=Oxford at the Clarendon Press |year=1933 |title=string }}</ref><ref>{{cite web |title=string (n.) |url=https://www.etymonline.com/search?q=string |website=Online Etymology Dictionary }}</ref> In 19th-Century typesetting, [[Compositor (typesetting)|compositors]] used the term "string" to denote a length of type printed on paper; the string would be measured to determine the compositor's pay.<ref>{{cite encyclopedia |encyclopedia=The Century Dictionary |author-link1=William Dwight Whitney |author-link2=Benjamin Eli Smith |first1=William Dwight |last1=Whitney |first2=Benjamin E. |last2=Smith |publisher=The Century Company |___location=New York |page=5994 |title=string }}</ref><ref name=Burchfield1986 /><ref>{{cite news |newspaper=[[Milwaukee Journal Sentinel|Milwaukee Sentinel]] |date=January 11, 1898 |title=Old Union's Demise |page=3 }}</ref>

Use of the word "string" to mean "a sequence of symbols or linguistic elements in a definite order" emerged from mathematics, [[symbolic logic]], and [[linguistic theory]] to speak about the [[formal system|formal]] behavior of symbolic systems, setting aside the symbols' meaning.<ref name=Burchfield1986>{{cite encyclopedia |title=string |encyclopedia=A Supplement to the Oxford English Dictionary |year=1986 |last=Burchfield |first=R.W. |publisher=Oxford at the Clarendon Press |author-link=Robert Burchfield }}</ref>

For example, logician [[C. I. Lewis]] wrote in 1918:<ref>{{cite book |title=A survey of symbolic logic |___location=Berkeley |publisher=University of California Press |year=1918 |page=355 |last=Lewis |first=C.I. |author-link=C.I. Lewis |url=https://archive.org/details/asurveyofsymboli00lewiuoft/page/355/mode/1up }}</ref>

For example, logician C. I. Lewis wrote in 1918:

<blockquote>

A mathematical system is any set of strings of recognisable marks in which some of the strings are taken initially and the remainder derived from these by operations performed according to rules which are independent of any meaning assigned to the marks. That a system should consist of 'marks' instead of sounds or odours is immaterial.

</blockquote>

According to [[Jean E. Sammet]], "the first realistic string handling and pattern matching language" for computers was [[COMIT]] in the 1950s, followed by the [[SNOBOL]] language of the early 1960s.<ref>{{cite journal |url=https://redirect.cs.umbc.edu/courses/undergraduate/331/resources/papers/sammet1972.pdf |journal=Communications of the ACM |first=Jean E. |last=Sammet |title=Programming Languages: History and Future |date=July 1972 |volume=15 |number=7 |doi=10.1145/361454.361485 |s2cid=2003242 }}</ref>

== String datatypes ==