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190+ 最終更新日時(UTC):
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192+ 2025年07月06日 07時11分54秒
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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 "> srand</ span > </ h1 >
216+ < div itemprop ="articleBody "> < p > < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="kt "> void</ span > < span class ="nf "> srand</ span > < span class ="p "> (</ span > < span class ="kt "> unsigned</ span > < span class ="n "> seed</ span > < span class ="p "> );</ span >
217+ </ code > </ pre > </ div >
218+ </ p >
219+ < h2 > 概要</ h2 >
220+ < p > < code > std::rand()</ code > 関数の疑似乱数生成器にシード値を渡す。</ p >
221+ < p > この関数が呼ばれる前に< code > std::rand()</ code > が呼ばれた場合、< code > srand(1)</ code > をシード値として実行される。</ p >
222+ < p > また、< code > stand()</ code > が同様の数値、つまりシード値が同じなら、< code > std::rand()</ code > は同様の数値を返す。</ p >
223+ < h2 > 備考</ h2 >
224+ < p > この関数はスレッドセーフではない。</ p >
225+ < p > 一般的には、< code > srand()</ code > を一度呼び出し、シード値を定義したあとに、再シードするべきではない。</ p >
226+ < p > また、< code > std::time</ code > は< code > std::time_t</ code > を返し、整数型である保証はされていない。</ p >
227+ < p > ただし、多くの環境では、整数値として定義されている。</ p >
228+ < h2 > 例</ h2 >
229+ < 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 >
230+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../ctime.html "> <ctime></ a > </ span > < span class ="cp "> </ span >
231+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../iostream.html "> <iostream></ a > </ span > < span class ="cp "> </ span >
232+
233+ < span class ="kt "> int</ span > < span class ="nf "> main</ span > < span class ="p "> ()</ span >
234+ < span class ="p "> {</ span >
235+ < 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 >
236+ < 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 >
237+ < span class ="p "> }</ span >
238+ </ code > </ pre > </ div >
239+ </ div > </ p >
240+ < h2 > 出力例</ h2 >
241+ < p > < pre > < code > 1373858591
242+ </ code > </ pre > </ p >
243+ < h2 > 関連項目</ h2 >
244+ < ul >
245+ < li > < code > rand</ code > :疑似乱数を生成する</ li >
246+ < li > < code > RAND_MAX</ code > :< code > std::rand()</ code > が返す最高値。</ li >
247+ < li > < code > time</ code > :時刻を取得する</ li >
248+ < li > < code > < a href ="../ctime/time_t.html "> time_t</ a > </ code > :UNIX時間を表すための型。</ li >
249+ </ ul > </ div >
250+
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