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In [[Computing]], a '''string''' (or '''string of characters''') is a data type used in most [[programming language]]s to represent text, and is the focus of this article.
The computing term ''string'' is also used in a broader sense to group a sequence of entities; for example, tokens in a language grammar, or a sequence of states in automata. See the theory of [[computation]].
=== Representations ==
A common representation is an [[array]] of characters. The length can be stored implicitly by using a special terminating character (often [[NUL]]) (the programming language [[C language|C]] uses this convention), or explicitly (for example by treating the first byte of the string as its length, a convention used in [[Pascal programming language|Pascal]]).▼
▲A common representation is an [[array]] of characters. The length can be stored implicitly by using a special terminating character (often [[NUL]]) (the programming language [[C language|C]] uses this convention), or explicitly (for example by treating the first byte of the string as its length, a convention used in [[Pascal]]).
Here is a NUL terminated string stored in a 10 [[Integral data types|byte]] buffer. NUL is the name for the character in [[ASCII]] which has the numeric value of zero.
<PRE>
x x x x x x x x x x
F R A N K 0 k f f w
x x x x x x x x x x
</PRE>
The above example is how "FRANK" would look in a 10 byte NUL terminated string. Characters after the 0 do not form part of the representation.
Of course, other representations are possible. Using [[tree]]s and [[list]]s make it easier to insert characters in the middle of the string.
=== String Processing ===
Strings are such a useful datatype that several languages have been designed in order to make string processing applications easy to write. Examples include:
* [[awk]]
* [[Icon programming language|Icon]]
* [[perl]]
* [[MUMPS programming language|MUMPS]]
* [[sed]]
* [[SNOBOL]]
Many [[UNIX]] utilities perform simple string manipulations and can be used to easily program some powerful string processing algorithms. Files and finite streams may be viewed as strings.
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