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}}</ref> A '''line comment''' ends at the end of the text line. In modern languages, a line comment starts with a delimiter but some older languages designate a column at which subsequent text is considered comment.<ref name="javadude000" /> Many languages support both block and line comments {{endash}} using different delimiters for each. For example, [[C (programming language)|C]], [[C++]] and their many derivatives support block comments delimited by <code>/*</code> and <code>*/</code> and line comments delimited by <code>//</code>. Other languages support only one type of comment.<ref name="javadude000" />
Comments can also be classified as either prologue or inline based on their position and content relative to program code. A '''prologue comment''' is a comment (or group of related comments) located near the top of an associated programming topic, such as before a symbol declaration or at the top of a file
<syntaxhighlight lang="c">
/*
* prologue block comment; if is about foo()
*/
bool foo() {
return true; /* inline block comment; if is about this return */
}
//
// prologue line comment; if is about bar()
//
bool bar() {
return false; // inline line comment; if is about this return
}
</syntaxhighlight>
==Examples of use==
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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
=== Integrate with development tools ===
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| publisher=Cambridge University Press
| isbn=978-1-397-80521-8
}}</ref> Examples include [[Javadoc]],
=== 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
Other examples include interpreter [[Directive (programming)|directives]]:
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<syntaxhighlight lang="c">
/***************************
* *
* This is the comment body. *
* *
</syntaxhighlight>
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==Tags==
Programmers often use one of select words {{endash}} also
Commonly used tags include:
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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]], [[
<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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<syntaxhighlight lang="AppleScript">
# line comment (in later versions)
(*
This program displays a greeting.
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====Fortran====
The following fixed-form [[Fortran
<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
<syntaxhighlight lang="ocaml">
codeLine(* comment level 1(*comment level 2*)*)
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====Pascal, Delphi====
▲As an alternative, for computers that do not support these characters, '(* ... *)' are allowed.<ref>{{cite book|author=Kathleen Jensen, Niklaus Wirth|year=1985|title=Pascal User Manual and Report|publisher=Springer-Verlag|isbn=0-387-96048-1}}</ref> In [[Niklaus Wirth]]'s more modern family of languages (including [[Modula-2]] and [[Oberon (programming language)|Oberon]]), comments are delimited by '(* ... *)'.<ref>{{cite book|author=Niklaus Wirth|year=1983|title=Programming in Modula-2|publisher=Springer-Verlag|isbn=0-387-15078-1}}</ref><ref>*{{cite book|author=Martin Reiser, Niklaus Wirth|year=1992|title=Programming in Oberon|publisher=Addison-Wesley|isbn=0-201-56543-9}}</ref> Comments can be nested. // can be included in a {} and {} can be included in a (**). For example:
<syntaxhighlight lang="pascal">
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