Empty string: Difference between revisions

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{{Short description|Unique string of length zero}}

{{Refimprove|date=November 2009}}

In [[formal language theory]], the '''empty string''', oralso known as the '''empty word''' or '''null string''', is the unique [[String (computer science)|string]] of length zero.

==Formal theory<span class="anchor" id="nullable symbol"></span>==

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|-

| <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]], [[PowerShell]], [[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]], [[PowerShell]], [[Python (programming language)|Python]], [[R (programming language)|R]], [[Ruby (programming language)|Ruby]], [[Smalltalk]], [[SQL]]

|-

| <code>character(0)</code>

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| [[Perl]]

|-

| <code>str()</code><ref>Another way to make an empty string is multiplying a string by 0 or a negative integer.</ref>

| <code>str()</code>

| [[Python (programming language)|Python]]

|-

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| <code><nowiki>[[]]</nowiki></code>

| [[Lua (programming language)|Lua]]

|-

| <code>str()“”</code>

<code>‘’</code>

<code>„”</code>

<code>‚‘</code>{{refn|All 'smart' quotation marks work as both opening and closing marks in any combination, except that single marks must be paired with single marks and double marks with double marks. For example {{code|"Hello, world„}} is valid. Guillemets are not supported. Note that the German-style low single quotation mark given here is {{Unichar|201A}}; the similar-looking character {{Unichar|2C}} does not function as a quotation mark. PowerShell's official documentation recommends using straight quotation marks.<ref>{{cite web |url=https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_quoting_rules?view=powershell-7.5 |title=about_Quoting_Rules – PowerShell |work=Microsoft Learn |access-date=26 August 2025 |url-status=live |archive-url=https://web.archive.org/web/20250814175659/https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_quoting_rules?view=powershell-7.5 |archive-date=2025-08-14 |quote=PowerShell treats smart quotation marks, also called typographic or curly quotes, as normal quotation marks for strings. Don't use smart quotation marks to enclose strings.}}</ref>}}

|[[PowerShell]]

|}

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* [[Concatenation theory]]

* [[String literal]]

* [[0]]

==References==