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{{Refimprove|date=February 2015}}

In [[computer programming]], '''trimming''' ('''trim''') or '''stripping''' ('''strip''') is a [[string (computer science)|string manipulation]] in which leading and trailing [[whitespace character|whitespace]] is removed from a [[string (computer science)|string]].

For example, the string (enclosed by apostrophes)

<syntaxhighlight lang=text>' this is a test '</syntaxhighlight>

would be changed, after trimming, to

<syntaxhighlight lang=text>'this is a test'</syntaxhighlight>

==Variants==

===Left or right trimming===

The most popular variants of the trim function strip only the beginning or end of the string. Typically named '''ltrim''' and '''rtrim''' respectively, or in the case of Python: '''lstrip''' and '''rstrip'''. C# uses '''TrimStart''' and '''TrimEnd''', and Common Lisp '''string-left-trim''' and '''string-right-trim'''. Pascal and Java do not have these variants built-in, although [[Object Pascal]] (Delphi) has '''TrimLeft''' and '''TrimRight''' functions.<ref>{{cite web|url=https://www.freepascal.org/docs-html/rtl/sysutils/trim.html |title=Trim |publisher=Freepascal.org |date=2013-02-02 |access-date=2013-08-24}}</ref>

===Whitespace character list parameterization===

Many trim functions have an optional parameter to specify a list of characters to trim, instead of the default whitespace characters. For example, PHP and Python allow this optional parameter, while Pascal and Java do not. With Common Lisp's <code>string-trim</code> function, the parameter (called ''character-bag'') is required. The C++ [[Boost library]] defines space characters according to [[Locale (computer software)|locale]], as well as offering variants with a [[predicate (computer programming)|predicate]] parameter (a [[functor]]) to select which characters are trimmed.

===Special empty string return value===

An uncommon variant of trim returns a special result if no characters remain after the trim operation. For example, [[Jakarta Project|Apache Jakarta]]'s '''StringUtils''' has a function called <code>stripToNull</code> which returns <code>null</code> in place of an empty string.

===Space normalization===

Space normalization is a related string manipulation where in addition to removing surrounding whitespace, any sequence of whitespace characters within the string is replaced with a single space. Space normalization is performed by the function named <code>Trim()</code> in spreadsheet applications (including [[Microsoft Excel|Excel]], [[OpenOffice.org Calc|Calc]], [[Gnumeric]], and [[Google Docs]]), and by the <code>normalize-space()</code> function in [[XSL Transformations|XSLT]] and [[XPath]],

===In-place trimming===

While most algorithms return a new (trimmed) string, some alter the original string [[in-place]]. Notably, the [[Boost library]] allows either in-place trimming or a trimmed copy to be returned.

==Definition of whitespace==
The characters which are considered whitespace varies between programming languages and implementations. For example, C traditionally only counts space, tab, line feed, and carriage return characters, while languages which support [[Unicode]] typically include all Unicode space characters. Some implementations also include [[ASCII]] control codes (non-printing characters) along with whitespace characters.

Java's trim method considers ASCII spaces and control codes as whitespace, contrasting with the Java <code>isWhitespace()</code> method,<ref>{{cite web|url=https://java.sun.com/j2se/1.5.0/docs/api/java/lang/Character.html#isWhitespace(char) |title=Character (Java 2 Platform SE 5.0) |publisher=Java.sun.com |access-date=2013-08-24}}</ref> which recognizes all Unicode space characters.

Delphi's Trim function considers characters U+0000 (NULL) through U+0020 (SPACE) to be whitespace.

=== Non-space blanks ===
The [[Braille Patterns]] Unicode block contains {{unichar|2800|Braille pattern blank|html=}}, a [[Braille]] pattern with no dots raised.
The Unicode standard explicitly states that it does not act as a space.

The [[Non-breaking space]] {{unichar|00A0|NO-BREAK SPACE|html=}} can also be treated as non-space for trimming purposes.

==Usage==
{{Main|Comparison of programming languages (string functions)#trim}}

==References==
{{Reflist}}

==External links==
*[https://www.tcl.tk/man/tcl8.4/TclCmd/string.htm#M46 Tcl: string trim]
*[https://blog.stevenlevithan.com/archives/faster-trim-javascript Faster JavaScript Trim] - compares various JavaScript trim implementations
*[http://webwidetutor.com/php/PHP-Change-String-value-behaviour-or-look-?id=8 php string cut and trimming]- php string cut and trimming

[[Category:Articles with example code]]
[[Category:String (computer science)]]

Trimming (computer programming) - Revision history

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