Comment (computer programming): Difference between revisions

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Comments can store [[metadata]] about the code. Common metadata includes the name of the original author and subsequent maintainers, dates when first written and modified, link to development and user documentation, and legal information such as [[copyright]] and [[software license]].

Some [[programming tools]] write metadata into the code as comments.<ref>See e.g., {{cite book |last=Wynne-Powell |first=Rod |year=2008 |title=Mac OS X for Photographers: Optimized Image Workflow for the Mac User |page=243 |publisher=Focal Press |___location=Oxford |isbn=978-0-240-52027-8 |url=https://archive.org/details/macosxforphotogr0000wynn}}</ref> For example, a [[version control]] tool might write metadata such as author, date and version number into each file when it's commitedcommitted to the repository.<ref>See e.g., {{cite book |last=Berlin |first=Daniel |year=2006 |title=Practical Subversion, Second Edition |page=168 |publisher=APress |___location=Berkeley |isbn=978-1-59059-753-8}}</ref>

=== Integrate with development tools ===

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| publisher=Cambridge University Press

| isbn=978-1-397-80521-8

}}</ref> Examples include [[Javadoc]], [[Ddoc]], [[Doxygen]], [[Visual Expert]] and [[PHPDoc]]. Forms of [[docstring]] are supported by [[Python (programming language)|Python]], [[Lisp (programming language)|Lisp]], [[Elixir (programming language)|Elixir]], and [[Clojure]].<ref>[https://clojure.github.io/clojure/clojure.core-api.html#clojure.core/defn Function definition with docstring in Clojure]</ref> [[C Sharp (programming language)|C#]], [[F Sharp (programming language)|F#]] and [[Visual Basic .NET]] implement a similar feature called "XML Comments" which are read by [[IntelliSense]] from the compiled [[.NET]] assembly.<ref>{{cite book|last=Murach|title=C# 2005|page=56}}</ref>

=== Visualization ===

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=== Extend language syntax ===

Occasionally, code that is formatted as a comment is overloaded to convey additional information to the translator, such as [[conditional comment]]scomments. As such, syntax that generally indicates a comment can actually represent program code; not comment code. Such syntax may be a practical way to maintain compatibility while adding additional functionality, but some regard such a solution as a [[kludge]].<ref>[[c2: HotComments]]</ref>

Other examples include interpreter [[Directive (programming)|directives]]:

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<syntaxhighlight lang="c">

/***************************\**

* *

* This is the comment body. *

* *

\ *****************************/

</syntaxhighlight>

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===Curly brace languages===

Many of the [[curly brace language]]s such as C, C++ and their many derivatives delimit a line comment with {{code|//}} and a block comment with {{code|/*}} and {{code|*/}}. Originally, C lacked the line comment, but it was added in [[C99]]. Notable languages include: C, C++, [[C# (programming language)|C#]], [[D (programming language)|D]], [[Java (programming language)|Java]], [[JavascriptJavaScript]] and [[Swift (programming language)|Swift]]. For example:

<syntaxhighlight lang="c">

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====APL====

[[APL (programming language)|APL]] uses <code>⍝</code> ("lamp") for a line comment. For example:

<syntaxhighlight lang="apl">

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====Fortran====

The following fixed-form [[Fortran IV]] code fragment shows that comment syntax is column-oriented. A letter <code>C</code> in the first column causes the entire line to be treated as a comment. In [[Fortran 77]], an asterisk in column 1 also indicates a comment.

<syntaxhighlight lang="fortranfixed">

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<syntaxhighlight lang="Fortran">

! A comment

program comment_test

print '(A)', 'Hello world' ! also a comment

end program

</syntaxhighlight>

Free-form Fortran, also introduced with Fortran 90, only supports this latter style of comment.

Although not a part of the Fortran Standard, many Fortran compilers offer an optional C-like [[preprocessor]] pass. This can be used to provide block comments:

<syntaxhighlight lang="Fortran">

#if 0

This is a block comment spanning

multiple lines.

#endif

program comment_test

print '(A)', 'Hello world' ! also a comment

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====OCaml====

[[OCaml]] supports nestable comments. For exmapleexample:

<syntaxhighlight lang="ocaml">

codeLine(* comment level 1(*comment level 2*)*)