You do not have permission to edit this page, for the following reasons:

This IP address has been blocked from editing Wikipedia.
This does not affect your ability to read Wikipedia pages.
Most people who see this message have done nothing wrong. Some kinds of blocks restrict editing from specific service providers or telecom companies in response to recent abuse or vandalism, and can sometimes affect other users who are unrelated to that abuse. Review the information below for assistance if you do not believe that you have done anything wrong.

The IP address or range 54.163.0.0/16 has been blocked (disabled) by ‪Blablubbs‬ for the following reason(s):

The IP address that you are currently using has been blocked because it is believed to be a web host provider or colocation provider. To prevent abuse, web hosts and colocation providers may be blocked from editing Wikipedia.
You will not be able to edit Wikipedia using a web host or colocation provider because it hides your IP address, much like a proxy or VPN.
We recommend that you attempt to use another connection to edit. For example, if you use a proxy or VPN to connect to the internet, turn it off when editing Wikipedia. If you edit using a mobile connection, try using a Wi-Fi connection, and vice versa. If you are using a corporate internet connection, switch to a different Wi-Fi network. If you have a Wikipedia account, please log in.
If you do not have any other way to edit Wikipedia, you will need to request an IP block exemption.

How to appeal if you are confident that your connection does not use a colocation provider's IP address:
If you are confident that you are not using a web host, you may appeal this block by adding the following text on your talk page: ((unblock|reason=Caught by a colocation web host block but this host or IP is not a web host. My IP address is _______. Place any further information here. ~~~~)). You must fill in the blank with your IP address for this block to be investigated. Your IP address can be determined here. Alternatively, if you wish to keep your IP address private you can use the unblock ticket request system. There are several reasons you might be editing using the IP address of a web host or colocation provider (such as if you are using VPN software or a business network); please use this method of appeal only if you think your IP address is in fact not a web host or colocation provider.

Administrators: The IP block exemption user right should only be applied to allow users to edit using web host in exceptional circumstances, and requests should usually be directed to the functionaries team via email. If you intend to give the IPBE user right, a CheckUser needs to take a look at the account. This can be requested most easily at SPI Quick Checkuser Requests. Unblocking an IP or IP range with this template is highly discouraged without at least contacting the blocking administrator.

This block will expire on 17:28, 10 March 2024.

Even when blocked, you will usually still be able to edit your user talk page, as well as email administrators and other editors.

For information on how to proceed, please read the FAQ for blocked users and the guideline on block appeals. The guide to appealing blocks may also be helpful.

Other useful links: Blocking policy · Help:I have been blocked
Your IP address is in a range that has been blocked on all Wikimedia Foundation wikis. The block was made by ‪Jon Kolbert‬. The reason given is Open proxy/Webhost: See the help page if you are affected .
- Start of block: 18:27, 12 November 2023
- Expiry of block: 18:27, 12 November 2028
Your current IP address is 54.163.179.242. The blocked range is 54.163.0.0/16. Please include all above details in any queries you make. If you believe you were blocked by mistake, you can find additional information and instructions in the No open proxies global policy. Otherwise, to discuss the block please post a request for review on Meta-Wiki. You could also send an email to the stewards VRT queue at stewards@wikimedia.org including all above details.

You can view and copy the source of this page:

((hatnote|The term ((green|((big|&nbsp;""&nbsp;)))) redirects here. For the printed character, see [[Quotation mark]].))
((Short description|Unique string of length zero))
((Refimprove|date=November 2009))
In [[formal language theory]], the '''empty string''', or '''empty word''', is the unique [[String (computer science)|string]] of length zero.

==Formal theory<span class="anchor" id="nullable symbol"></span>==
Formally, a string is a finite, ordered sequence of [[character (symbol)|characters]] such as 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.
There is only one empty string, because two strings are only different if they have different lengths or a different sequence of symbols.
In formal treatments,<ref>((cite journal |first1=John |last1=Corcoran |first2=William |last2=Frank |first3=Michael |last3=Maloney |title=String theory |journal=Journal of Symbolic Logic |volume=39 |issue=4 |year=1974 |pages=625–637 |doi=10.2307/2272846 |jstor=2272846|s2cid=2168826 ))</ref> the empty string is denoted with '''[[ε]]''' or sometimes '''[[Λ]]''' or '''[[λ]]'''.

The empty string should not be confused with the empty language [[∅]], which is a [[formal language]] (i.e. a set of strings) that contains no strings, not even the empty string.

The empty string has several properties:
* |ε| = 0. Its [[string (computer science)#Formal theory|string length]] is zero.
* ε ⋅ s = s ⋅ ε = s. The empty string is the [[identity element]] of the [[concatenation]] operation. The set of all strings forms a [[free monoid]] with respect to ⋅ and ε.
* ε<sup>R</sup> = ε. Reversal of the empty string produces the empty string.
* <math>\forall c \in s: P(c)</math>. Statements that are about all characters in a string are [[vacuous truth|vacuously true]].
* The empty string precedes any other string under [[lexicographical order]], because it is the shortest of all strings.<ref>[http://cs.fit.edu/~ryan/cse1002/lectures/lexicographic.pdf CSE1002 Lecture Notes – Lexicographic]</ref>

In [[context-free grammar]]s, a [[production (computer science)|production rule]] that allows a [[symbol (logic)|symbol]] to produce the empty string is known as an ε-production, and the symbol is said to be "nullable".

==Use in programming languages==
In most [[programming language]]s, strings are a [[data type]]. Strings are typically stored at distinct [[memory address]]es (locations). Thus, the same string (for example, the empty string) may be stored in two or more places in memory. 

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

Even a string of length zero can require memory to store it, depending on the format being used. In most programming languages, the empty string is distinct from a [[null reference]] (or null pointer) because a null reference points to no string at all, not even the empty string.
<!---A null reference is likely to cause an error if one tries to perform any operation on it, but an empty string is less likely to do so.--->
The empty string is a legitimate string, upon which most string operations should work. Some languages treat some or all of the following in similar ways: empty strings, null references, the integer 0, the floating point number 0, the Boolean value [[False (logic)|false]], the [[ASCII]] character [[null character|NUL]], or other such values.

The empty string is usually represented similarly to other strings. In implementations with string terminating character ([[null-terminated string]]s or plain text lines), the empty string is indicated by the immediate use of this terminating character.

Different functions, methods, macros, or [[Programming idiom|idioms]] exist for checking if a string is empty in different languages.((examples|date=July 2023))

{| class="wikitable"
|-
! λ representation
! Programming languages
|-
| <code>""</code>
| [[C (programming language)|C]], [[C Sharp (programming language)|C#]], [[C++]], [[Go (programming language)|Go]], [[Haskell (programming language)|Haskell]], [[Java (programming language)|Java]], [[JavaScript]], [[Julia (programming language)|Julia]], [[Lua (programming language)|Lua]], [[MUMPS|M]], [[Objective-C]] (as a C string), [[OCaml]], [[Perl]], [[PHP]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], [[Scala (programming language)|Scala]], [[Standard ML]], [[Swift (programming language)|Swift]], [[Tcl]], [[Visual Basic .NET]]
|-
| <code>&#39;&#39;</code>
| [[APL (programming language)|APL]], [[Delphi (programming language)|Delphi]], [[JavaScript]], [[Lua (programming language)|Lua]], [[MATLAB]], [[Pascal (programming language)|Pascal]], [[Perl]], [[PHP]], [[Python (programming language)|Python]], [[R (programming language)|R]], [[Ruby (programming language)|Ruby]], [[Smalltalk]], [[SQL]]
|-
| <code>character(0)</code>
| [[R (programming language)|R]]((Refn|There are two ways to create "empty strings" in R; the other is listed here as <code>""</code>. <code>character(0)</code> creates empty character vectors, which will output 0 when counted.))
|-
| <code>{'\0'}</code>
| [[C (programming language)|C]], [[C++]], [[Objective-C]] (as a C string)
|-
| <code>std::string()</code>
| [[C++]]
|-
| <code>""s</code>
| [[C++]] (since the [[C++14|2014 standard]])
|-
| <code>@""</code>
| [[Objective-C]] (as a constant <code>NSString</code> object)
|-
| <code>[NSString string]</code>
| [[Objective-C]] (as a new <code>NSString</code> object)
|-
| <code>q(), qq()</code>
| [[Perl]]
|-
| <code>str()</code>
| [[Python (programming language)|Python]]
|-
| <code>%{}</code><br /><code>%()</code>
| [[Ruby (programming language)|Ruby]]
|-
| <code>String::new()</code><ref>((Cite web |title=String in std::string - Rust |url=https://doc.rust-lang.org/std/string/struct.String.html#method.new |access-date=2022-11-30 |website=doc.rust-lang.org))</ref>
| [[Rust (programming language)|Rust]]
|-
| <code>string.Empty</code>
| [[C Sharp (programming language)|C#]], [[VB.NET|Visual Basic .NET]]
|- 
| <code>String.make 0 '-'</code>
| [[OCaml]]
|- 
| <code>{}</code>
| [[Tcl]]
|-
| <code><nowiki>[[]]</nowiki></code>
| [[Lua (programming language)|Lua]]
|}

=== Examples of empty strings ===
((Expand section|date=March 2010))
The empty string is a syntactically valid representation of [[0 (number)|zero]] in [[positional notation]] (in any base), which does not contain [[leading zero]]s. Since the empty string does not have a standard visual representation outside of formal language theory, the number zero is traditionally represented by a single [[decimal digit]] '''0''' instead.

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

Empty lines of text show the empty string. This can occur from two consecutive [[End of line|EOLs]], as often occur in [[text file]]s, and this is sometimes used in [[text processing]] to separate [[paragraph]]s, e.g. in [[MediaWiki]].

==See also==
*[[Empty set]]
*[[Null-terminated string]]
*[[Concatenation theory]]

==References==
((Reflist))

((DEFAULTSORT:Empty String))
[[Category:Formal languages]]
[[Category:String (computer science)]]
[[Category:Zero (linguistics)]]

Pages transcluded onto the current version of this page (help):

Empty string (edit)
Template:Ambox (view source) (template editor protected)
Template:Big (view source) (template editor protected)
Template:Category handler (view source) (protected)
Template:Cite journal (view source) (protected)
Template:Cite web (view source) (protected)
Template:Delink (view source) (protected)
Template:Example needed (view source) (semi-protected)
Template:Examples (view source) (semi-protected)
Template:Expand section (view source) (template editor protected)
Template:Find sources mainspace (view source) (template editor protected)
Template:Fix (view source) (protected)
Template:Fix/category (view source) (protected)
Template:Green (view source) (template editor protected)
Template:Hatnote (view source) (template editor protected)
Template:Large (view source) (template editor protected)
Template:Main other (view source) (protected)
Template:More citations needed (view source) (template editor protected)
Template:Pagetype (view source) (protected)
Template:Refimprove (view source) (template editor protected)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Template:Refn (view source) (template editor protected)
Template:SDcat (view source) (protected)
Template:Short description (view source) (protected)
Template:Short description/lowercasecheck (view source) (protected)
Module:Arguments (view source) (protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Delink (view source) (protected)
Module:Disambiguation/templates (view source) (protected)
Module:Find sources (view source) (template editor protected)
Module:Find sources/config (view source) (template editor protected)
Module:Find sources/links (view source) (template editor protected)
Module:Find sources/templates/Find sources mainspace (view source) (template editor protected)
Module:Hatnote (view source) (template editor protected)
Module:Hatnote/styles.css (view source) (template editor protected)
Module:Message box (view source) (protected)
Module:Message box/ambox.css (view source) (protected)
Module:Message box/configuration (view source) (protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Pagetype (view source) (protected)
Module:Pagetype/config (view source) (protected)
Module:Pagetype/disambiguation (view source) (protected)
Module:Pagetype/setindex (view source) (protected)
Module:Pagetype/softredirect (view source) (protected)
Module:SDcat (view source) (protected)
Module:String (view source) (protected)
Module:Unsubst (view source) (protected)
Module:Wikitext Parsing (view source) (protected)
Module:Yesno (view source) (protected)

Return to Empty string.

Retrieved from "https://en.wikipedia.org/wiki/Empty_string"