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+ 最終更新日時(UTC):
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+ < span itemprop ="datePublished " content ="2025-06-04T03:06:39 ">
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+ 2025年06月04日 03時06分39秒
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+ </ span >
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+ < br />
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+ < span itemprop ="author " itemscope itemtype ="http://schema.org/Person ">
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+ < span itemprop ="name "> Akira Takahashi</ span >
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+ が更新
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+ < span class ="fa fa-fw fa-clock-o fa-flip-horizontal "> </ span > 履歴
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+ </ a >
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+ < a class ="edit " target ="_blank " href ="https://github.com/cpprefjp/site/edit/master/reference/ranges/cartesian_product_view/begin.md ">
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+ < span class ="fa fa-fw fa-pencil "> </ span > 編集
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+ < div class ="row ">
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+ < div class ="col-sm-12 content-body ">
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+
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+ < div class ="identifier-type "> function</ div > < div class ="header "> <ranges></ div > < h1 itemprop ="name "> < span class ="namespace " title ="namespace std::ranges "> std::ranges::</ span > < span class ="class " title ="class cartesian_product_view "> cartesian_product_view::</ span > < span class ="token "> begin</ span > < span class ="cpp cpp23 " title ="C++23で追加 "> (C++23)</ span > </ h1 >
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+ < div itemprop ="articleBody "> < p > < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="k "> constexpr</ span > < span class ="n "> < i > iterator</ i > </ span > < span class ="o "> <</ span > < span class ="nb "> false</ span > < span class ="o "> ></ span > < span class ="n "> begin</ span > < span class ="p "> ()</ span >
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+ < span class ="n "> requires</ span > < span class ="p "> (</ span > < span class ="o "> !</ span > < span class ="n "> simple</ span > < span class ="o "> -</ span > < span class ="n "> < a href ="../view.html "> view</ a > </ span > < span class ="o "> <</ span > < span class ="n "> First</ span > < span class ="o "> ></ span > < span class ="o "> ||</ span > < span class ="p "> ...</ span > < span class ="o "> ||</ span > < span class ="o "> !</ span > < span class ="n "> simple</ span > < span class ="o "> -</ span > < span class ="n "> < a href ="../view.html "> view</ a > </ span > < span class ="o "> <</ span > < span class ="n "> Vs</ span > < span class ="o "> ></ span > < span class ="p "> );</ span > < span class ="c1 "> // (1) C++23</ span >
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+
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+ < span class ="k "> constexpr</ span > < span class ="n "> < i > iterator</ i > </ span > < span class ="o "> <</ span > < span class ="nb "> true</ span > < span class ="o "> ></ span > < span class ="n "> begin</ span > < span class ="p "> ()</ span > < span class ="k "> const</ span > < span class ="p "> ;</ span > < span class ="c1 "> // (2) C++23</ span >
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+ </ code > </ pre > </ div >
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+ </ p >
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+ < h2 > 概要</ h2 >
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+ < p > 先頭要素を指すイテレータを取得する。</ p >
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+ < h2 > 効果</ h2 >
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+ < ul >
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+ < li > (1), (2) : 以下と等価
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+ < br />
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+ < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="k "> return</ span > < span class ="n "> iterator</ span > < span class ="o "> <</ span > < span class ="n "> Const</ span > < span class ="o "> ></ span > < span class ="p "> (</ span > < span class ="o "> *</ span > < span class ="k "> this</ span > < span class ="p "> ,</ span > < span class ="n "> < a href ="../../tuple/tuple.html "> tuple</ a > </ span > < span class ="o "> -</ span > < span class ="n "> transform</ span > < span class ="p "> (</ span > < span class ="n "> < a href ="../begin.html "> ranges::begin</ a > </ span > < span class ="p "> ,</ span > < span class ="n "> bases_</ span > < span class ="p "> ));</ span >
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+ </ code > </ pre > </ div >
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+ </ li >
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+ </ ul >
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+ < p > ここで、< code > iterator</ code > は説明専用のイテレータクラスであり、< code > tuple-transform</ code > は説明専用の関数で、tupleの各要素に関数を適用する。< code > Const</ code > は各< a class ="cpprefjp-defined-word " data-desc ="同名の関数を異なる引数・テンプレート・制約などで複数定義すること。または同名の関数の集合 "> オーバーロード</ a > に応じて< code > false</ code > または< code > true</ code > となる。</ p >
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+ < h2 > 例</ h2 >
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+ < p > < div class ="yata " id ="5fb6e2c26a2626331c593e1139baeccdc72d0b0a "> < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../../ranges.html "> <ranges></ a > </ span > < span class ="cp "> </ span >
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+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../../vector.html "> <vector></ a > </ span > < span class ="cp "> </ span >
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+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../../list.html "> <list></ a > </ span > < span class ="cp "> </ span >
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+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../../print.html "> <print></ a > </ span > < span class ="cp "> </ span >
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+
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+ < span class ="kt "> int</ span > < span class ="nf "> main</ span > < span class ="p "> ()</ span > < span class ="p "> {</ span >
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+ < span class ="n "> < a href ="../../vector/vector.html "> std::vector</ a > </ span > < span class ="o "> <</ span > < span class ="kt "> int</ span > < span class ="o "> ></ span > < span class ="n "> v</ span > < span class ="o "> =</ span > < span class ="p "> {</ span > < span class ="mi "> 1</ span > < span class ="p "> ,</ span > < span class ="mi "> 2</ span > < span class ="p "> };</ span >
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+ < span class ="n "> < a href ="../../list/list.html "> std::list</ a > </ span > < span class ="o "> <</ span > < span class ="kt "> char</ span > < span class ="o "> ></ span > < span class ="n "> l</ span > < span class ="o "> =</ span > < span class ="p "> {</ span > < span class ="sc "> 'a'</ span > < span class ="p "> ,</ span > < span class ="sc "> 'b'</ span > < span class ="p "> };</ span >
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+
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+ < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> ranges</ span > < span class ="o "> ::</ span > < span class ="n "> cartesian_product_view</ span > < span class ="n "> cv</ span > < span class ="p "> {</ span > < span class ="n "> v</ span > < span class ="p "> ,</ span > < span class ="n "> l</ span > < span class ="p "> };</ span >
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+
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+ < span class ="k "> auto</ span > < span class ="n "> it</ span > < span class ="o "> =</ span > < span class ="n "> cv</ span > < span class ="p "> .</ span > < span class ="n "> < span style ="color:#ff0000 "> begin</ span > </ span > < span class ="p "> ();</ span >
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+
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+ < span class ="c1 "> // 最初の要素を出力</ span >
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+ < span class ="n "> < a href ="../../print/println.html "> std::println</ a > </ span > < span class ="p "> (</ span > < span class ="s "> "first element: {}"</ span > < span class ="p "> ,</ span > < span class ="o "> *</ span > < span class ="n "> it</ span > < span class ="p "> );</ span >
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+ < span class ="p "> }</ span >
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+ </ code > </ pre > </ div >
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+ </ div > </ p >
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+ < h3 > 出力</ h3 >
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+ < p > < pre > < code > first element: (1, 'a')
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+ </ code > </ pre > </ p >
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+ < h2 > バージョン</ h2 >
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+ < h3 > 言語</ h3 >
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+ < ul >
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+ < li > C++23</ li >
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+ </ ul >
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+ < h3 > 処理系</ h3 >
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+ < ul >
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+ < li > < a href ="../../../implementation.html#clang "> Clang</ a > : 16.0 < span aria-label ="検証済 " role ="img " title ="検証済 "> ✅</ span > </ li >
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+ < li > < a href ="../../../implementation.html#gcc "> GCC</ a > : 13.2 < span aria-label ="検証済 " role ="img " title ="検証済 "> ✅</ span > </ li >
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+ < li > < a href ="../../../implementation.html#visual_cpp "> Visual C++</ a > : 2022 Update 7 < span aria-label ="検証済 " role ="img " title ="検証済 "> ✅</ span > </ li >
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+ </ ul >
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+ < h2 > 参照</ h2 >
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+ < ul >
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+ < li > < a href ="https://timsong-cpp.github.io/cppwp/n4950/range.cartesian " target ="_blank "> N4950 26.7.33 Cartesian product view</ a > </ li >
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