What Does Use Token Mean On Chase

Unique string of length zip

In formal linguistic communication theory, the
empty string, or
empty give-and-take, is the unique string of length zero.


Formal theory


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Formally, a string is a finite, ordered sequence of characters such equally 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 1 empty string, because ii strings are only unlike if they have unlike lengths or a different sequence of symbols. In formal treatments,[ane]
the empty cord is denoted with
ε
or sometimes
Λ
or
λ.

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

The empty cord has several backdrop:

  • |ε| = 0. Its cord length is zero.
  • ε ⋅ s = s ⋅ ε = s. The empty string is the identity chemical element of the chain functioning. The set of all strings forms a free monoid with respect to ⋅ and ε.
  • εR
    = ε. Reversal of the empty string produces the empty cord.
  • The empty string precedes any other string under lexicographical guild, considering it is the shortest of all strings.[2]

In context-complimentary grammars, a production rule that allows a symbol to produce the empty string is known every bit an ε-production, and the symbol is said to be “nullable”.

Utilise in programming languages

[edit]

In most programming languages, strings are a information blazon. Strings are typically stored at distinct retention addresses (locations). Thus, the aforementioned string (for instance, the empty string) may be stored in ii or more places in memory.

In this way, there could exist multiple empty strings in memory, in contrast with the formal theory definition, for which there is only i possible empty cord. However, a cord comparing office would signal that all of these empty strings are equal to each other.

Even a string of length zero tin require memory to store information technology, depending on the format being used. In most programming languages, the empty string is singled-out from a zip reference (or null pointer) because a aught reference points to no cord at all, not even the empty string. The empty string is a legitimate string, upon which well-nigh string operations should work. Some languages treat some or all of the following in similar ways: empty strings, zippo references, the integer 0, the floating signal 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 (nothing-terminated strings or plain text lines), the empty string is indicated by the immediate use of this terminating character.

λ representation Programming languages
"" C, C#, C++, Go, Haskell, Coffee, JavaScript, Julia, Lua, M, Objective-C (as a C string), OCaml, Perl, PHP, Python, Scarlet, Scala, Standard ML, Swift, Tcl, Visual Basic .NET
'' APL, Delphi, JavaScript, Lua, MATLAB, Pascal, Perl, PHP, Python, R, Ruby, Smalltalk, SQL
character(0) R[3]
{'\0'} C, C++, Objective-C (as a C string)
std::string() C++
""due south C++ (since the 2014 standard)
@"" Objective-C (equally a abiding
NSString
object)
[NSString string] Objective-C (as a new
NSString
object)
q(), qq() Perl
str() Python
%{}

%()
Ruby
String::new()
[four]
Rust
string.Empty C#, Visual Bones .Internet
String.make 0 '-' OCaml
{} Tcl
[[]] Lua

Examples of empty strings

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The empty cord is a syntactically valid representation of zero in positional annotation (in any base), which does not contain leading zeros. Since the empty string does non have a standard visual representation outside of formal linguistic communication theory, the number zero is traditionally represented past a single decimal digit
0
instead.

Zilch-filled memory area, interpreted equally a zero-terminated cord, is an empty string.

Empty lines of text show the empty string. This tin occur from 2 consecutive EOLs, every bit often occur in text files, and this is sometimes used in text processing to separate paragraphs, due east.thousand. in MediaWiki.

See besides

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  • Empty gear up
  • Null-terminated string
  • Concatenation theory

References

[edit]


  1. ^


    Corcoran, John; Frank, William; Maloney, Michael (1974). “String theory”.
    Journal of Symbolic Logic.
    39
    (4): 625–637. doi:10.2307/2272846. JSTOR 2272846. S2CID 2168826.



  2. ^

    CSE1002 Lecture Notes – Lexicographic

  3. ^

    At that place are 2 means to create “empty strings” in R; the other is listed hither equally
    "".
    character(0)
    creates empty character vectors, which will output 0 when counted.

  4. ^


    “Cord in std::string – Rust”.
    doc.rust-lang.org
    . Retrieved
    2022-11-30
    .




Source: https://en.wikipedia.org/wiki/Empty_string

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