1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
|
<!DOCTYPE html>
<html lang="en" dir="ltr" class="client-nojs">
<head>
<title>Comments - cppreference.com</title>
<meta charset="UTF-8" />
<meta name="generator" content="MediaWiki 1.21.2" />
<link rel="alternate" type="application/x-wiki" title="Edit" href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit" />
<link rel="edit" title="Edit" href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit" />
<link rel="shortcut icon" href="../../favicon.ico" />
<link rel="search" type="application/opensearchdescription+xml" href="../../mwiki/opensearch_desc.php" title="cppreference.com (en)" />
<link rel="EditURI" type="application/rsd+xml" href="http://en.cppreference.com/mwiki/api.php?action=rsd" />
<link rel="alternate" type="application/atom+xml" title="cppreference.com Atom feed" href="http://en.cppreference.com/mwiki/index.php?title=Special:RecentChanges&feed=atom" />
<link rel="stylesheet" href="../../mwiki/load.php%3Fdebug=false&lang=en&modules=ext.gadget.ColiruCompiler%257Cext.rtlcite%257Cmediawiki.legacy.commonPrint%252Cshared%257Cskins.cppreference2&only=styles&skin=cppreference2&*.css" />
<meta name="ResourceLoaderDynamicStyles" content="" />
<link rel="stylesheet" href="../../mwiki/load.php%3Fdebug=false&lang=en&modules=site&only=styles&skin=cppreference2&*.css" />
<style>a:lang(ar),a:lang(ckb),a:lang(fa),a:lang(kk-arab),a:lang(mzn),a:lang(ps),a:lang(ur){text-decoration:none}#toc{display:none}.editsection{display:none}
/* cache key: mwiki1-mwiki_en_:resourceloader:filter:minify-css:7:472787eddcf4605d11de8c7ef047234f */</style>
<script src="../../mwiki/load.php%3Fdebug=false&lang=en&modules=startup&only=scripts&skin=cppreference2&*"></script>
<script>if(window.mw){
mw.config.set({"wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"c/comment","wgTitle":"c/comment","wgCurRevisionId":76087,"wgArticleId":13869,"wgIsArticle":true,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":[],"wgBreakFrames":false,"wgPageContentLanguage":"en","wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy","wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgMonthNamesShort":["","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"],"wgRelevantPageName":"c/comment","wgRestrictionEdit":[],"wgRestrictionMove":[]});
}</script><script>if(window.mw){
mw.loader.implement("user.options",function(){mw.user.options.set({"ccmeonemails":0,"cols":80,"date":"default","diffonly":0,"disablemail":0,"disablesuggest":0,"editfont":"default","editondblclick":0,"editsection":0,"editsectiononrightclick":0,"enotifminoredits":0,"enotifrevealaddr":0,"enotifusertalkpages":1,"enotifwatchlistpages":0,"extendwatchlist":0,"externaldiff":0,"externaleditor":0,"fancysig":0,"forceeditsummary":0,"gender":"unknown","hideminor":0,"hidepatrolled":0,"imagesize":2,"justify":0,"math":1,"minordefault":0,"newpageshidepatrolled":0,"nocache":0,"noconvertlink":0,"norollbackdiff":0,"numberheadings":0,"previewonfirst":0,"previewontop":1,"quickbar":5,"rcdays":7,"rclimit":50,"rememberpassword":0,"rows":25,"searchlimit":20,"showhiddencats":0,"showjumplinks":1,"shownumberswatching":1,"showtoc":0,"showtoolbar":1,"skin":"cppreference2","stubthreshold":0,"thumbsize":2,"underline":2,"uselivepreview":0,"usenewrc":0,"watchcreations":0,"watchdefault":0,"watchdeletion":0,
"watchlistdays":3,"watchlisthideanons":0,"watchlisthidebots":0,"watchlisthideliu":0,"watchlisthideminor":0,"watchlisthideown":0,"watchlisthidepatrolled":0,"watchmoves":0,"wllimit":250,"variant":"en","language":"en","searchNs0":true,"searchNs1":false,"searchNs2":false,"searchNs3":false,"searchNs4":false,"searchNs5":false,"searchNs6":false,"searchNs7":false,"searchNs8":false,"searchNs9":false,"searchNs10":false,"searchNs11":false,"searchNs12":false,"searchNs13":false,"searchNs14":false,"searchNs15":false,"gadget-ColiruCompiler":1});;},{},{});mw.loader.implement("user.tokens",function(){mw.user.tokens.set({"editToken":"+\\","patrolToken":false,"watchToken":false});;},{},{});
/* cache key: mwiki1-mwiki_en_:resourceloader:filter:minify-js:7:ca03345b1e2c4d90a25d968753a73b92 */
}</script>
<script>if(window.mw){
mw.loader.load(["mediawiki.page.startup","mediawiki.legacy.wikibits","mediawiki.legacy.ajax"]);
}</script>
<style type="text/css">/*<![CDATA[*/
.source-c {line-height: normal;}
.source-c li, .source-c pre {
line-height: normal; border: 0px none white;
}
/**
* GeSHi Dynamically Generated Stylesheet
* --------------------------------------
* Dynamically generated stylesheet for c
* CSS class: source-c, CSS id:
* GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
* (http://qbnz.com/highlighter/ and http://geshi.org/)
* --------------------------------------
*/
.c.source-c .de1, .c.source-c .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.c.source-c {font-family:monospace;}
.c.source-c .imp {font-weight: bold; color: red;}
.c.source-c li, .c.source-c .li1 {font-weight: normal; vertical-align:top;}
.c.source-c .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.c.source-c .li2 {font-weight: bold; vertical-align:top;}
.c.source-c .kw1 {color: #0000dd;}
.c.source-c .kw2 {color: #0000ff;}
.c.source-c .kw3 {color: #0000dd;}
.c.source-c .kw4 {color: #0000ff;}
.c.source-c .co1 {color: #909090;}
.c.source-c .co2 {color: #339900;}
.c.source-c .coMULTI {color: #ff0000; font-style: italic;}
.c.source-c .es0 {color: #008000; font-weight: bold;}
.c.source-c .es1 {color: #008000; font-weight: bold;}
.c.source-c .es2 {color: #008000; font-weight: bold;}
.c.source-c .es3 {color: #008000; font-weight: bold;}
.c.source-c .es4 {color: #008000; font-weight: bold;}
.c.source-c .es5 {color: #008000; font-weight: bold;}
.c.source-c .br0 {color: #008000;}
.c.source-c .sy0 {color: #008000;}
.c.source-c .sy1 {color: #000080;}
.c.source-c .sy2 {color: #000040;}
.c.source-c .sy3 {color: #000040;}
.c.source-c .sy4 {color: #008080;}
.c.source-c .st0 {color: #008000;}
.c.source-c .nu0 {color: #000080;}
.c.source-c .nu6 {color:#000080;}
.c.source-c .nu8 {color:#000080;}
.c.source-c .nu12 {color:#000080;}
.c.source-c .nu16 {color:#000080;}
.c.source-c .nu17 {color:#000080;}
.c.source-c .nu18 {color:#000080;}
.c.source-c .nu19 {color:#000080;}
.c.source-c .ln-xtra, .c.source-c li.ln-xtra, .c.source-c div.ln-xtra {background-color: #ffc;}
.c.source-c span.xtra { display:block; }
/*]]>*/
</style><!--[if lt IE 7]><style type="text/css">body{behavior:url("/mwiki/skins/cppreference2/csshover.min.htc")}</style><![endif]--></head>
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_comment skin-cppreference2 action-view cpp-navbar">
<!-- header -->
<div id="mw-head" class="noprint">
<div id="cpp-head-first-base">
<div id="cpp-head-first">
<h5><a href="../../index.html">
cppreference.com </a></h5>
<div id="cpp-head-search">
<!-- 0 -->
<div id="p-search">
<h5><label for="searchInput">Search</label></h5>
<form action="http://en.cppreference.com/mwiki/index.php" id="searchform">
<input type='hidden' name="title" value="Special:Search"/>
<div id="simpleSearch">
<input name="search" title="Search cppreference.com [f]" accesskey="f" id="searchInput" /> <button type="submit" name="button" title="Search the pages for this text" id="searchButton"><img src="../../mwiki/skins/cppreference2/images/search-ltr.png%3F303" alt="Search" /></button> </div>
</form>
</div>
<!-- /0 -->
</div>
<div id="cpp-head-personal">
<!-- 0 -->
<div id="p-personal" class="">
<span id="pt-createaccount"><a href="http://en.cppreference.com/mwiki/index.php?title=Special:UserLogin&returnto=c%2Fcomment&type=signup">Create account</a></span> <div class="menu">
<ul>
<li id="pt-login"><a href="http://en.cppreference.com/mwiki/index.php?title=Special:UserLogin&returnto=c%2Fcomment" title="You are encouraged to log in; however, it is not mandatory [o]" accesskey="o">Log in</a></li> </ul>
</div>
</div>
<!-- /0 -->
</div>
</div>
</div>
<div id="cpp-head-second-base">
<div id="cpp-head-second">
<div id="cpp-head-tools-left">
<!-- 0 -->
<div id="p-namespaces" class="vectorTabs">
<h5>Namespaces</h5>
<ul>
<li id="ca-nstab-main" class="selected"><span><a href="comment.html" title="View the content page [c]" accesskey="c">Page</a></span></li>
<li id="ca-talk"><span><a href="http://en.cppreference.com/w/Talk:c/comment" title="Discussion about the content page [t]" accesskey="t">Discussion</a></span></li>
</ul>
</div>
<!-- /0 -->
<!-- 1 -->
<div id="p-variants" class="vectorMenu emptyPortlet">
<h5><span>Variants</span><a href="comment.html#"></a></h5>
<div class="menu">
<ul>
</ul>
</div>
</div>
<!-- /1 -->
</div>
<div id="cpp-head-tools-right">
<!-- 0 -->
<div id="p-views" class="vectorTabs">
<h5>Views</h5>
<ul>
<li id="ca-view" class="selected"><span><a href="comment.html" >View</a></span></li>
<li id="ca-edit"><span><a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit" title="You can edit this page. Please use the preview button before saving [e]" accesskey="e">Edit</a></span></li>
<li id="ca-history" class="collapsible"><span><a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=history" title="Past revisions of this page [h]" accesskey="h">History</a></span></li>
</ul>
</div>
<!-- /0 -->
<!-- 1 -->
<div id="p-cactions" class="vectorMenu emptyPortlet">
<h5><span>Actions</span><a href="comment.html#"></a></h5>
<div class="menu">
<ul>
</ul>
</div>
</div>
<!-- /1 -->
</div>
</div>
</div>
</div>
<!-- /header -->
<!-- content -->
<div id="cpp-content-base">
<div id="content">
<a id="top"></a>
<div id="mw-js-message" style="display:none;"></div>
<!-- firstHeading -->
<h1 id="firstHeading" class="firstHeading">Comments</h1>
<!-- /firstHeading -->
<!-- bodyContent -->
<div id="bodyContent">
<!-- tagline -->
<div id="siteSub">From cppreference.com</div>
<!-- /tagline -->
<!-- subtitle -->
<div id="contentSub"><span class="subpages">< <a href="../c.html" title="c">c</a></span></div>
<!-- /subtitle -->
<!-- bodycontent -->
<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../c.html" title="c"> C</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
<tr class="t-nv"><td colspan="5"> <a href="language.1.html" title="c/language"> Language</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="header.html" title="c/header"> headers</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="types.html" title="c/types"> Type support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="memory.html" title="c/memory"> Dynamic memory management</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="error.html" title="c/error"> Error handling</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="program.html" title="c/program"> Program utilities</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="variadic.html" title="c/variadic"> Variadic function support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="chrono.html" title="c/chrono"> Date and time utilities</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="string.html" title="c/string"> Strings library</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="algorithm.html" title="c/algorithm"> Algorithms</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="numeric.html" title="c/numeric"> Numerics</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="io.html" title="c/io"> Input/output support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="locale.html" title="c/locale"> Localization support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="thread.html" title="c/thread"> Thread support</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="atomic.html" title="c/atomic"> Atomic operations</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="experimental.html" title="c/experimental"><span class="t-lines"><span>Technical Specifications</span></span></a></div></div></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:c/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="language.1.html" title="c/language"> C language</a></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="language/basic_concepts.html" title="c/language/basic concepts"> Basic Concepts</a><div class="t-navbar-menu"><div><div style="display:inline-block">
<div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <strong class="selflink"> comments</strong></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/ascii.html" title="c/language/ascii"> ASCII</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/translation_phases.html" title="c/language/translation phases"> Translation phases</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/identifier.html" title="c/language/identifier">identifier</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/scope.html" title="c/language/scope">scope</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/lifetime.html" title="c/language/lifetime">lifetime</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/name_space.html" title="c/language/name space">lookup and name spaces</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/compatible_type.html" title="c/language/type">type</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/arithmetic_types.html" title="c/language/arithmetic types">arithmetic types</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/main_function.html" title="c/language/main function">the main() function</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="language/memory_model.html" title="c/language/memory model">memory model and data races</a></td></tr>
</table></div>
</div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:c/language/basics/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>Comments serve as a sort of in-code documentation. When inserted into a program, they are effectively ignored by the compiler; they are solely intended to be used as notes by the humans that read source code.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="comment.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="comment.html#C-style"><span class="tocnumber">2</span> <span class="toctext">C-style</span></a></li>
<li class="toclevel-1"><a href="comment.html#C.2B.2B-style"><span class="tocnumber">3</span> <span class="toctext">C++-style</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="comment.html#Notes"><span class="tocnumber">4</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="comment.html#Example"><span class="tocnumber">5</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="comment.html#References"><span class="tocnumber">6</span> <span class="toctext">References</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="comment.html#See_Also"><span class="tocnumber">7</span> <span class="toctext">See Also</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>/*</b></code> <span class="t-spar">comment</span> <code><b>*/</b></code>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>//</b></code> <span class="t-spar">comment</span>\n
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-c99">(since C99)</span>
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<div class="t-li1"><span class="t-li">1)</span> Often known as "C-style" or "multi-line" comments.</div>
<div class="t-li1"><span class="t-li">2)</span> Often known as "C++-style" or "single-line" comments.</div>
<p>All comments are removed from the program at <a href="language/translation_phases.html" title="c/language/translation phases">translation phase 3</a> by replacing each comment with a single whitespace character.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=2" title="Edit section: C-style">edit</a>]</span> <span class="mw-headline" id="C-style">C-style</span></h3>
<p>C-style comments are usually used to comment large blocks of text or small fragments of code; however, they can be used to comment single lines. To insert text as a C-style comment, simply surround the text with <code>/*</code> and <code>*/</code>. C-style comments tell the compiler to ignore all content between <code>/*</code> and <code>*/</code>. Although it is not part of the C standard, <code>/**</code> and <code>*/</code> are often used to indicate documentation blocks; this is legal because the second asterisk is simply treated as part of the comment.
</p><p>Except within a <a href="language/character_constant.html" title="c/language/character constant">character constant</a>, a <a href="language/string_literal.html" title="c/language/string literal">string literal</a>, or a comment, the characters <code>/*</code> introduce a comment. The contents of such a comment are examined only to identify multibyte characters and to find the characters <code>*/</code> that terminate the comment. C-style comments cannot be nested.
</p>
<table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<h3> <span class="mw-headline" id="C.2B.2B-style">C++-style</span></h3>
<p>C++-style comments are usually used to comment single lines of text or code; however, they can be placed together to form multi-line comments. To insert text as a C++-style comment, simply precede the text with <code>//</code> and follow the text with the new line character. C++-style comments tell the compiler to ignore all content between <code>//</code> and a new line.
</p><p>Except within a <a href="language/character_constant.html" title="c/language/character constant">character constant</a>, a <a href="language/string_literal.html" title="c/language/string literal">string literal</a>, or a comment, the characters <code>//</code>
introduce a comment that includes all multibyte characters up to, but not including, the next new-line character. The contents of such a comment are examined only to identify
multibyte characters and to find the new-line character that terminates the comment. C++-style comments can be nested:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co1">// y = f(x); // invoke algorithm</span></pre></div></div>
<p>A C-style comment may appear within a C++-style comment:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co1">// y = f(x); /* invoke algorithm */</span></pre></div></div>
<p>A C++-style comment may appear within a C-style comment; this is a mechanism for excluding a small block of source code:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="coMULTI">/*
y = f(x); // invoke algorithms
z = g(x);
*/</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=4" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>Because comments <a href="language/translation_phases.html" title="c/language/translation phases">are removed</a> before the preprocessor stage, a macro cannot be used to form a comment and an unterminated C-style comment doesn't spill over from an #include'd file.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="coMULTI">/* An attempt to use a macro to form a comment. */</span>
<span class="coMULTI">/* But, a space replaces characters "//". */</span>
<span class="co2">#ifndef DEBUG</span>
<span class="co2">#define PRINTF //</span>
<span class="co2">#else</span>
<span class="co2">#define PRINTF printf</span>
<span class="co2">#endif</span>
...
<span class="me1">PRINTF</span><span class="br0">(</span><span class="st0">"Error in file %s at line %i<span class="es1">\n</span>"</span>, __FILE__, __LINE__<span class="br0">)</span><span class="sy4">;</span></pre></div></div>
<p>Besides commenting out, other mechanisms used for source code exclusion are:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#if 0</span>
<a href="io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span><span class="st0">"this will not be compiled"</span><span class="br0">)</span><span class="sy4">;</span>
<span class="coMULTI">/* no conflict with C-style comments */</span>
<span class="co1">// no conflict with C++-style comments</span>
<span class="co2">#endif</span></pre></div></div>
<p>and
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">if</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span>
<a href="io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span><span class="st0">"this will be compiled but not be executed"</span><span class="br0">)</span><span class="sy4">;</span>
<span class="coMULTI">/* no conflict with C-style comments */</span>
<span class="co1">// no conflict with C++-style comments</span>
<span class="br0">}</span></pre></div></div>
<p>The introduction of // comments in C99 was a breaking change in some rare circumstances:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1">a <span class="sy1">=</span> b <span class="co1">//*divisor:*/ c</span>
<span class="sy2">+</span> d<span class="sy4">;</span> <span class="coMULTI">/* C89 compiles a = b / c + d;
C99 compiles a = b + d; */</span></pre></div></div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=5" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="coMULTI">/*
C-style comments can contain
multiple lines.
*/</span>
 
<span class="coMULTI">/* Or, just one line. */</span>
 
<span class="co1">// C++-style comments can comment one line.</span>
 
<span class="co1">// Or, they can</span>
<span class="co1">// be strung together.</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co1">// The below code won't be run</span>
<span class="co1">// return 1;</span>
 
<span class="co1">// The below code will be run</span>
<span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p><br />
</p>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=6" title="Edit section: References">edit</a>]</span> <span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011):
</li></ul>
<dl><dd><ul><li> 6.4.9 Comments (p: 75)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999):
</li></ul>
<dl><dd><ul><li> 6.4.9 Comments (p: 66)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990):
</li></ul>
<dl><dd><ul><li> 3.1.9 Comments
</li></ul>
</dd></dl>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=edit&section=7" title="Edit section: See Also">edit</a>]</span> <span class="mw-headline" id="See_Also">See Also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../cpp/comments.html" title="cpp/comments" class="mw-redirect">C++ documentation</a></span> for <span class="t-dsc-see-tt"><span>Comments</span></span></div>
</td></tr>
</table></div>
</div>
<!--
NewPP limit report
Preprocessor visited node count: 859/1000000
Preprocessor generated node count: 4190/1000000
Post‐expand include size: 24591/2097152 bytes
Template argument size: 5178/2097152 bytes
Highest expansion depth: 13/40
Expensive parser function count: 0/100
-->
<!-- Saved in parser cache with key mwiki1-mwiki_en_:pcache:idhash:13869-0!*!0!!en!*!* and timestamp 20150211154902 -->
</div> <!-- /bodycontent -->
<!-- printfooter -->
<div class="printfooter">
Retrieved from "<a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&oldid=76087">http://en.cppreference.com/mwiki/index.php?title=c/comment&oldid=76087</a>" </div>
<!-- /printfooter -->
<!-- catlinks -->
<div id='catlinks' class='catlinks catlinks-allhidden'></div> <!-- /catlinks -->
<div class="visualClear"></div>
<!-- debughtml -->
<!-- /debughtml -->
</div>
<!-- /bodyContent -->
</div>
</div>
<!-- /content -->
<!-- footer -->
<div id="cpp-footer-base" class="noprint">
<div id="footer">
<div id="cpp-navigation">
<h5>Navigation</h5>
<ul>
<li id="n-Support-us"><a href="http://www.cppreference.com/support" rel="nofollow">Support us</a></li><li id="n-recentchanges"><a href="http://en.cppreference.com/w/Special:RecentChanges" title="A list of recent changes in the wiki [r]" accesskey="r">Recent changes</a></li><li id="n-FAQ"><a href="http://en.cppreference.com/w/Cppreference:FAQ">FAQ</a></li><li id="n-Offline-version"><a href="http://en.cppreference.com/w/Cppreference:Archives">Offline version</a></li> </ul>
</div>
<div id="cpp-toolbox">
<h5><span>Toolbox</span><a href="comment.html#"></a></h5>
<ul>
<li id="t-whatlinkshere"><a href="http://en.cppreference.com/w/Special:WhatLinksHere/c/comment" title="A list of all wiki pages that link here [j]" accesskey="j">What links here</a></li><li id="t-recentchangeslinked"><a href="http://en.cppreference.com/w/Special:RecentChangesLinked/c/comment" title="Recent changes in pages linked from this page [k]" accesskey="k">Related changes</a></li><li id="t-upload"><a href="http://upload.cppreference.com/w/Special:Upload" title="Upload files [u]" accesskey="u">Upload file</a></li><li id="t-specialpages"><a href="http://en.cppreference.com/w/Special:SpecialPages" title="A list of all special pages [q]" accesskey="q">Special pages</a></li><li id="t-print"><a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&printable=yes" rel="alternate" title="Printable version of this page [p]" accesskey="p">Printable version</a></li><li id="t-permalink"><a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&oldid=76087" title="Permanent link to this revision of the page">Permanent link</a></li><li id="t-info"><a href="http://en.cppreference.com/mwiki/index.php?title=c/comment&action=info">Page information</a></li> </ul>
</div>
<div id="cpp-languages">
<div><ul><li>In other languages</li></ul></div>
<div><ul>
<li class="interwiki-ar"><a href="http://ar.cppreference.com/w/c/comment" title="c/comment" lang="ar" hreflang="ar">العربية</a></li><li class="interwiki-cs"><a href="http://cs.cppreference.com/w/c/comment" title="c/comment" lang="cs" hreflang="cs">Česky</a></li><li class="interwiki-de"><a href="http://de.cppreference.com/w/c/comment" title="c/comment" lang="de" hreflang="de">Deutsch</a></li><li class="interwiki-es"><a href="http://es.cppreference.com/w/c/comment" title="c/comment" lang="es" hreflang="es">Español</a></li><li class="interwiki-fr"><a href="http://fr.cppreference.com/w/c/comment" title="c/comment" lang="fr" hreflang="fr">Français</a></li><li class="interwiki-it"><a href="http://it.cppreference.com/w/c/comment" title="c/comment" lang="it" hreflang="it">Italiano</a></li><li class="interwiki-ja"><a href="http://ja.cppreference.com/w/c/comment" title="c/comment" lang="ja" hreflang="ja">日本語</a></li><li class="interwiki-ko"><a href="http://ko.cppreference.com/w/c/comment" title="c/comment" lang="ko" hreflang="ko">한국어</a></li><li class="interwiki-pl"><a href="http://pl.cppreference.com/w/c/comment" title="c/comment" lang="pl" hreflang="pl">Polski</a></li><li class="interwiki-pt"><a href="http://pt.cppreference.com/w/c/comment" title="c/comment" lang="pt" hreflang="pt">Português</a></li><li class="interwiki-ru"><a href="http://ru.cppreference.com/w/c/comment" title="c/comment" lang="ru" hreflang="ru">Русский</a></li><li class="interwiki-tr"><a href="http://tr.cppreference.com/w/c/comment" title="c/comment" lang="tr" hreflang="tr">Türkçe</a></li><li class="interwiki-zh"><a href="http://zh.cppreference.com/w/c/comment" title="c/comment" lang="zh" hreflang="zh">中文</a></li> </ul></div>
</div>
<ul id="footer-info">
<li id="footer-info-lastmod"> This page was last modified on 9 February 2015, at 09:52.</li>
<li id="footer-info-viewcount">This page has been accessed 576 times.</li>
</ul>
<ul id="footer-places">
<li id="footer-places-privacy"><a href="http://en.cppreference.com/w/Cppreference:Privacy_policy" title="Cppreference:Privacy policy">Privacy policy</a></li>
<li id="footer-places-about"><a href="http://en.cppreference.com/w/Cppreference:About" title="Cppreference:About">About cppreference.com</a></li>
<li id="footer-places-disclaimer"><a href="http://en.cppreference.com/w/Cppreference:General_disclaimer" title="Cppreference:General disclaimer">Disclaimers</a></li>
</ul>
<ul id="footer-icons" class="noprint">
<li id="footer-poweredbyico">
<a href="http://www.mediawiki.org/"><img src="../../mwiki/skins/common/images/poweredby_mediawiki_88x31.png" alt="Powered by MediaWiki" width="88" height="31" /></a> <a href="http://qbnz.com/highlighter/"><img src="../../../upload.cppreference.com/mwiki/images/2/2b/powered_by_geshi_88x31.png" alt="Powered by GeSHi" height="31" width="88" /></a> <a href="http://www.tigertech.net/referral/cppreference.com"><img src="../../../upload.cppreference.com/mwiki/images/9/94/powered_by_tigertech_88x31.png" alt="Hosted by Tiger Technologies" height="31" width="88" /></a> </li>
</ul>
<div style="clear:both">
</div>
</div>
</div>
<!-- /footer -->
<script>if(window.mw){
mw.loader.state({"site":"loading","user":"missing","user.groups":"ready"});
}</script>
<script src="../../mwiki/load.php%3Fdebug=false&lang=en&modules=skins.cppreference2&only=scripts&skin=cppreference2&*"></script>
<script>if(window.mw){
mw.loader.load(["mediawiki.action.view.postEdit","mediawiki.user","mediawiki.page.ready","mediawiki.searchSuggest","mediawiki.hidpi","ext.gadget.ColiruCompiler"], null, true);
}</script>
<script src="../../mwiki/load.php%3Fdebug=false&lang=en&modules=site&only=scripts&skin=cppreference2&*"></script>
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");
document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-2828341-1']);
_gaq.push(['_setDomainName', 'cppreference.com']);
_gaq.push(['_trackPageview']);
</script><!-- Served in 0.088 secs. -->
</body>
<!-- Cached 20150211165643 -->
</html>
|
