Create A Museum Exhibit Project

Unique string of length zero

In formal linguistic communication theory, the empty string, or empty discussion, is the unique string of length aught.

Formal theory [edit]

Formally, a string is a finite, ordered sequence of characters such every bit letters, digits or spaces. The empty string is the special case where the sequence has length zero, so there are no symbols in the string. In that location is only one empty cord, because two strings are only unlike if they have different lengths or a different sequence of symbols. In formal treatments,^[1] the empty string is denoted with ε or sometimes Λ or λ.

The empty cord should not be confused with the empty language ∅, which is a formal linguistic communication (i.east. a set of strings) that contains no strings, not fifty-fifty the empty string.

The empty string has several backdrop:

|ε| = 0. Its string length is zero.
ε ⋅ s = s ⋅ ε = southward. The empty string is the identity chemical element of the chain performance. The gear up of all strings forms a gratuitous monoid with respect to ⋅ and ε.
ε^R = ε. Reversal of the empty cord produces the empty string.
The empty string precedes any other string under lexicographical order, considering it is the shortest of all strings.^[ii]

In context-free grammars, a production dominion that allows a symbol to produce the empty string is known every bit an ε-production, and the symbol is said to be "nullable".

Use in programming languages [edit]

In most programming languages, strings are a data blazon. Strings are typically stored at distinct memory addresses (locations). Thus, the aforementioned cord (for example, the empty string) may exist stored in two or more places in retentivity.

In this way, in that location could be multiple empty strings in memory, in contrast with the formal theory definition, for which there is only one possible empty cord. However, a string comparison function would point that all of these empty strings are equal to each other.

Fifty-fifty a string of length zip can require retentivity to store it, depending on the format being used. In about programming languages, the empty string is singled-out from a null reference (or cypher pointer) because a null reference points to no string at all, non even the empty string. The empty cord is a legitimate string, upon which most string operations should work. Some languages care for some or all of the following in similar ways: empty strings, cipher references, the integer 0, the floating point number 0, the Boolean value false, the ASCII character NUL, or other such values.

The empty string is usually represented similarly to other strings. In implementations with string terminating character (zilch-terminated strings or obviously text lines), the empty string is indicated by the immediate utilise of this terminating grapheme.

λ representation	Programming languages
`""`	C, C#, C++, Go, Haskell, Java, JavaScript, Julia, Lua, Yard, Objective-C (every bit a C string), OCaml, Perl, PHP, Python, Cerise, Scala, Standard ML, Swift, Tcl, Visual Basic .NET
`''`	APL, Delphi, JavaScript, Lua, MATLAB, Pascal, Perl, PHP, Python, R, Reddish, Smalltalk, SQL
`character(0)`	R^[three]
`{'\0'}`	C, C++, Objective-C (as a C string)
`std::string()`	C++
`""due south`	C++ (since the 2014 standard)
`@""`	Objective-C (as a constant `NSString` object)
`[NSString cord]`	Objective-C (equally a new `NSString` object)
`q(), qq()`	Perl
`str()`	Python
`%{}` `%()`	Ruby
`cord.Empty`	C#, Visual Basic .Internet
`String.make 0 '-'`	OCaml
`{}`	Tcl
`[[]]`	Lua

Examples of empty strings [edit]

This section needs expansion. Y'all can help by calculation to it. (March 2010)

The empty string is a syntactically valid representation of nix in positional notation (in any base), which does not contain leading zeros. Since the empty string does not have a standard visual representation exterior of formal language theory, the number zippo is traditionally represented by a single decimal digit 0 instead.

Zero-filled memory surface area, interpreted as a null-terminated string, is an empty string.

Empty lines of text testify the empty string. This can occur from two consecutive EOLs, as often occur in text files, and this is sometimes used in text processing to divide paragraphs, e.1000. in MediaWiki.

Come across besides [edit]

Empty gear up
Null-terminated string
Chain theory

References [edit]

^ Corcoran, John; Frank, William; Maloney, Michael (1974). "String theory". Journal of Symbolic Logic. 39 (4): 625–637. doi:10.2307/2272846. JSTOR 2272846.
^ CSE1002 Lecture Notes – Lexicographic
^ There are ii ways to create "empty strings" in R; the other is listed here every bit "". character(0) creates empty grapheme vectors, which will output 0 when counted.