1+ <!doctype html>
2+ < html class ="cpprefjp " lang ="ja " itemscope ="" itemtype ="http://schema.org/WebPage ">
3+ < head >
4+
5+
6+ <!-- Google tag (gtag.js) -->
7+ < script async src ="https://www.googletagmanager.com/gtag/js?id=G-NXNBNVBTJS "> </ script >
8+ < script >
9+ window . dataLayer = window . dataLayer || [ ] ;
10+ function gtag ( ) { dataLayer . push ( arguments ) ; }
11+ gtag ( 'js' , new Date ( ) ) ;
12+
13+ gtag ( 'config' , 'G-NXNBNVBTJS' ) ;
14+ </ script >
15+
16+
17+ < meta charset ="UTF-8 ">
18+
19+ < title > rand - cpprefjp C++日本語リファレンス</ title >
20+
21+ < meta name ="viewport " content ="width=device-width,initial-scale=1 ">
22+ < meta name ="keywords " content ="
23+ C++,標準ライブラリ,リファレンス,ドキュメント,STL,std,cstdlib,std,function
24+ ">
25+ < meta name ="title " content ="rand - cpprefjp C++日本語リファレンス " />
26+ < meta itemprop ="name " content ="rand - cpprefjp C++日本語リファレンス " />
27+ < meta property ="og:title " content ="rand - cpprefjp C++日本語リファレンス " />
28+ < meta property ="og:url " content ="https://cpprefjp.github.io/reference/cstdlib/rand.html " />
29+ < meta property ="og:site_name " content ="cpprefjp - C++日本語リファレンス " />
30+ < meta property ="og:type " content ="article " />
31+ < meta property ="og:description " content ="`0`から`RAND_MAX`までの値の疑似乱数を返す。 " />
32+ < meta name ="twitter:card " content ="summary " />
33+ < meta name ="twitter:title " content ="rand - cpprefjp C++日本語リファレンス " />
34+ < meta name ="twitter:url " content ="https://cpprefjp.github.io/reference/cstdlib/rand.html " />
35+ < meta name ="twitter:description " content ="`0`から`RAND_MAX`までの値の疑似乱数を返す。 " />
36+
37+
38+ < link rel ="alternate " type ="application/atom+xml " title ="Atom " href ="https://cpprefjp.github.io/rss.xml " />
39+
40+
41+ < link rel ="apple-touch-icon " sizes ="180x180 " href ="../../static/favicons/apple-touch-icon.png?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 ">
42+ < link rel ="icon " type ="image/png " sizes ="32x32 " href ="../../static/favicons/favicon-32x32.png?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 ">
43+ < link rel ="icon " type ="image/png " sizes ="16x16 " href ="../../static/favicons/favicon-16x16.png?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 ">
44+ < link rel ="manifest " href ="../../manifest.json?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 ">
45+ < meta name ="theme-color " content ="#f5f8fc ">
46+
47+ < link rel ="stylesheet " href ="../../static/pygments/default.css?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 ">
48+ <!-- <link rel="stylesheet" href="../../static/css/root.css"> -->
49+
50+
51+
52+
53+
54+ < link href ="../../static/kunai/css/kunai-stage-0.css?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 " rel ="stylesheet ">
55+ < link href ="../../static/kunai/css/kunai-stage-1.css?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 " rel ="stylesheet ">
56+ < link href ="../../static/kunai/css/kunai-stage-2.css?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 " rel ="stylesheet ">
57+ < link href ="../../static/kunai/css/kunai-stage-3.css?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 " rel ="stylesheet ">
58+
59+ < script type ="text/javascript " src ="../../static/kunai/js/kunai-vendor.js?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 "> </ script >
60+ < script type ="text/javascript " src ="../../static/kunai/js/kunai.js?cachebust=77dc81f1a0fc7ba1be2bc06336653840aa3f2e20 "> </ script >
61+
62+ < script type ="text/javascript ">
63+ document . addEventListener ( 'DOMContentLoaded' , function ( ) {
64+ var kn = new Kunai ;
65+ kn . cpprefjp ( ) ;
66+ } ) ;
67+ </ script >
68+
69+ </ head >
70+ < body >
71+ < header data-kunai-mdinfo ="{"meta": {"header": ["cstdlib"], "namespace": ["std"], "id-type": ["function"]}, "sources": [{"id": "ce96b5e1535c9a4347617a9bf3f78bdfc46bda9a", "source": "#include <cstdlib>\n#include <ctime>\n#include <iostream>\n\nint main() \n{\n std::srand(std::time(0)); // \u73fe\u5728\u6642\u523b\u3092\u7591\u4f3c\u4e71\u6570\u306e\u30b7\u30fc\u30c9\u5024\u3068\u3059\u308b\u3002\n std::cout << std::rand() << '\\n';\n}\n"}], "page_id": ["reference", "cstdlib", "rand"]} ">
72+ < nav class ="navbar navbar-default " role ="navigation ">
73+ < div class ="container-fluid ">
74+ < div class ="navbar-header ">
75+ < button type ="button " class ="navbar-toggle collapsed " data-toggle ="collapse " data-target ="#navbar-collapse ">
76+ < span class ="sr-only "> Toggle navigation</ span >
77+ < span class ="icon-bar "> </ span >
78+ < span class ="icon-bar "> </ span >
79+ < span class ="icon-bar "> </ span >
80+ </ button >
81+ < a class ="navbar-brand " href ="../../index.html ">
82+ < div class ="title-wrapper clearfix ">
83+ < div class ="title "> cpprefjp - C++日本語リファレンス</ div >
84+ </ div >
85+ </ a >
86+ </ div >
87+
88+ < div class ="collapse navbar-collapse " id ="navbar-collapse ">
89+ < ul class ="nav navbar-nav navbar-right ">
90+ < li >
91+ < div class ="google-search ">
92+
93+
94+ < script >
95+ ( function ( ) {
96+ var cx = '013316413321391058734:ji_u66hl7hq' ;
97+ var gcse = document . createElement ( 'script' ) ;
98+ gcse . type = 'text/javascript' ;
99+ gcse . async = true ;
100+ gcse . src = ( document . location . protocol == 'https:' ? 'https:' : 'http:' ) +
101+ '//www.google.com/cse/cse.js?cx=' + cx ;
102+ var s = document . getElementsByTagName ( 'script' ) [ 0 ] ;
103+ s . parentNode . insertBefore ( gcse , s ) ;
104+ } ) ( ) ;
105+ </ script >
106+ < div class ="gcse-search "> </ div >
107+
108+
109+ </ div >
110+ </ li >
111+ < li >
112+ < a href ="https://github.com/cpprefjp/site "> GitHub Project</ a >
113+ </ li >
114+ </ ul >
115+ </ div >
116+ </ div >
117+ </ nav >
118+ </ header >
119+
120+ < main id ="main " role ="main ">
121+ < div class ="container-fluid ">
122+ < div class ="row ">
123+ < div class ="col-sm-9 col-sm-push-3 " itemscope itemtype ="http://schema.org/Article ">
124+ < div class ="row ">
125+ < div class ="col-sm-12 google-search-result ">
126+ < gcse:searchresults > </ gcse:searchresults >
127+ </ div >
128+ </ div >
129+ < div class ="row ">
130+ < div class ="col-sm-12 content-header ">
131+
132+ < ol class ="breadcrumb ">
133+
134+ < li itemscope itemtype ="http://www.schema.org/SiteNavigationElement ">
135+ < span >
136+
137+ < a href ="../../index.html " itemprop ="url ">
138+
139+ < i class ="fa fa-fw fa-home "> </ i >
140+
141+ </ a >
142+
143+ </ span >
144+ </ li >
145+
146+ < li itemscope itemtype ="http://www.schema.org/SiteNavigationElement ">
147+ < span >
148+
149+ < a href ="../../reference.html " itemprop ="url ">
150+
151+ < span itemprop ="name "> リファレンス</ span >
152+
153+ </ a >
154+
155+ </ span >
156+ </ li >
157+
158+ < li itemscope itemtype ="http://www.schema.org/SiteNavigationElement ">
159+ < span >
160+
161+ < a href ="../../reference/cstdlib.html " itemprop ="url ">
162+
163+ < span itemprop ="name "> cstdlib</ span >
164+
165+ </ a >
166+
167+ </ span >
168+ </ li >
169+
170+ < li class ="active " itemscope itemtype ="http://www.schema.org/SiteNavigationElement ">
171+ < span >
172+
173+
174+ < span itemprop ="name "> rand</ span >
175+
176+
177+ </ span >
178+ </ li >
179+
180+ </ ol >
181+ < div class ="crsearch "> </ div >
182+
183+ </ div >
184+ </ div >
185+ < div class ="row ">
186+ < div class ="col-sm-12 edit-button ">
187+
188+
189+ < p class ="text-right "> < small >
190+ 最終更新日時(UTC):
191+ < span itemprop ="datePublished " content ="2025-07-06T07:36:28 ">
192+ 2025年07月06日 07時36分28秒
193+ </ span >
194+ < br />
195+ < span itemprop ="author " itemscope itemtype ="http://schema.org/Person ">
196+ < span itemprop ="name "> K10-K10</ span >
197+ </ span >
198+ が更新
199+ </ small > </ p >
200+
201+
202+ < p class ="text-right ">
203+ < a class ="history " target ="_blank " href ="https://github.com/cpprefjp/site/commits/master/reference/cstdlib/rand.md ">
204+ < span class ="fa fa-fw fa-clock-o fa-flip-horizontal "> </ span > 履歴
205+ </ a >
206+ < a class ="edit " target ="_blank " href ="https://github.com/cpprefjp/site/edit/master/reference/cstdlib/rand.md ">
207+ < span class ="fa fa-fw fa-pencil "> </ span > 編集
208+ </ a >
209+ </ p >
210+ </ div >
211+ </ div >
212+ < div class ="row ">
213+ < div class ="col-sm-12 content-body ">
214+
215+ < div class ="identifier-type "> function</ div > < div class ="header "> <cstdlib></ div > < h1 itemprop ="name "> < span class ="namespace " title ="namespace std "> std::</ span > < span class ="token "> rand</ span > </ h1 >
216+ < div itemprop ="articleBody "> < h2 > 概要</ h2 >
217+ < p > < code > 0</ code > から< code > RAND_MAX</ code > までの値の疑似乱数を返す。</ p >
218+ < p > < code > < a href ="srand.html "> std::srand()</ a > </ code > 関数はこの関数の疑似乱数生成器で使用するシード値を決定する。</ p >
219+ < p > もし< code > < a href ="srand.html "> std::srand()</ a > </ code > の前に、< code > std::rand()</ code > が使用された場合、< code > srand(1)</ code > として生成される。</ p >
220+ < p > シード値が同じなら、< code > std::rand()</ code > も同じ値を返す。</ p >
221+ < p > また、標準ライブラリの複数の関数で< code > std::rand()</ code > 関数が呼び出される場合がある。</ p >
222+ < p > これは実装に依存している。</ p >
223+ < p > この関数がスレッドセーフであるかどうかも実装に依存している。</ p >
224+ < h2 > 備考</ h2 >
225+ < p > この関数の疑似乱数の品質は保証されていない。</ p >
226+ < p > より安全な乱数を使いたい場合は< code > random</ code > ライブラリなどを使用したほうが良い。</ p >
227+ < h2 > 例</ h2 >
228+ < p > < div class ="yata " id ="ce96b5e1535c9a4347617a9bf3f78bdfc46bda9a "> < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../cstdlib.html "> <cstdlib></ a > </ span > < span class ="cp "> </ span >
229+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../ctime.html "> <ctime></ a > </ span > < span class ="cp "> </ span >
230+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../iostream.html "> <iostream></ a > </ span > < span class ="cp "> </ span >
231+
232+ < span class ="kt "> int</ span > < span class ="nf "> main</ span > < span class ="p "> ()</ span >
233+ < span class ="p "> {</ span >
234+ < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> srand</ span > < span class ="p "> (</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> time</ span > < span class ="p "> (</ span > < span class ="mi "> 0</ span > < span class ="p "> ));</ span > < span class ="c1 "> // 現在時刻を疑似乱数のシード値とする。</ span >
235+ < span class ="n "> < a href ="../iostream/cout.html "> std::cout</ a > </ span > < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> rand</ span > < span class ="p "> ()</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span > < span class ="p "> ;</ span >
236+ < span class ="p "> }</ span >
237+ </ code > </ pre > </ div >
238+ </ div > </ p >
239+ < h2 > 出力例</ h2 >
240+ < p > < pre > < code > 1373858591
241+ </ code > </ pre > </ p >
242+ < h2 > 関連項目</ h2 >
243+ < ul >
244+ < li > < code > < a href ="srand.html "> srand()</ a > </ code > :この関数の疑似乱数生成器で使用するシード値を決定する。</ li >
245+ < li > < code > < span href ="https://cpprefjp.github.io/reference/cstdlib "> RAND_MAX</ span > </ code > :この関数で返される疑似乱数の最大値。</ li >
246+ </ ul > </ div >
247+
248+ </ div >
249+ </ div >
250+ </ div >
251+
252+
253+ < div id ="sidebar " class ="col-sm-3 col-sm-pull-9 ">
254+ </ div >
255+
256+
257+ </ div >
258+ </ div >
259+ </ main >
260+ < footer class ="footer navbar navbar-default ">
261+ < div class ="container-fluid ">
262+ < p > < small >
263+ 本サイトの情報は、
264+ < a href ="https://creativecommons.org/licenses/by/3.0/deed.ja " rel ="nofollow "> クリエイティブ・コモンズ 表示 3.0 非移植 ライセンス(CC BY)</ a >
265+ の下に提供されています。
266+ </ small > </ p >
267+ </ div >
268+ </ footer >
269+ </ body >
270+ </ html >
0 commit comments