std::ranges::find_last, std::ranges::find_last_if, std::ranges::find_last_if_not

 

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外部庫

 

演算法庫

有約束演算法與針對範圍的演算法 (C++20)
有約束的演算法，例如 ranges::copy、 ranges::sort 等……
執行策略 (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
非修改序列操作 批次操作 for_each for_each_n (C++17) 搜尋操作 all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n 修改序列操作 複製操作 copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) 交換操作 swap iter_swap swap_ranges 變換操作 replacereplace_if transform replace_copyreplace_copy_if 生成操作 fill fill_n generate generate_n 移除操作 removeremove_if unique remove_copyremove_copy_if unique_copy 順序變換操作 reverse reverse_copy rotate rotate_copy random_shuffleshuffle (C++17 前)(C++11) shift_leftshift_right (C++20)(C++20) 取樣操作 sample (C++17)	排序及相關操作 劃分操作 partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) 排序操作 sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element 二分搜尋操作 （於已劃分範圍上） lower_bound upper_bound equal_range binary_search 集合操作（於已排序範圍上） includes set_union set_intersection set_difference set_symmetric_difference 歸併操作（於已排序範圍上） merge inplace_merge 堆操作 push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) 最小/最大值操作 max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) 字典序比較操作 lexicographical_compare lexicographical_compare_three_way (C++20) 排列操作 next_permutation prev_permutation is_permutation (C++11) C 庫 qsort bsearch
數值操作
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
未初始化記憶體上的操作
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

受約束演算法

此選單中的所有名稱均屬於名稱空間 std::ranges

非修改序列操作

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

修改序列操作

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

劃分操作

is_partitioned    partition_point    partition    partition_copy    stable_partition

排序操作

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

二分查詢操作（在已排序的範圍內）

lower_bound         upper_bound         binary_search      equal_range

集合操作（於已排序範圍上）

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

堆操作

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

最小/最大值操作

max max_element         min min_element         minmax minmax_element     clamp

排列操作

is_permutation      next_permutation    prev_permutation

摺疊操作

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

數值操作 iota (C++23)             隨機數生成 generate_random (C++26)

對未初始化儲存的操作

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

返回型別

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

定義於標頭檔案 <algorithm>
呼叫簽名 (Call signature)
	(1)
template< std::forward_iterator I, std::sentinel_for<I> S,           class T,           class Proj = std::identity > requires std::indirect_binary_predicate              <ranges::equal_to, std::projected<I, Proj>, const T*> constexpr ranges::subrange<I>     find_last( I first, S last, const T& value, Proj proj = {} );			(C++23 起) （直到 C++26）
template< std::forward_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           class T = std::projected_value_t<I, Proj> > requires std::indirect_binary_predicate              <ranges::equal_to, std::projected<I, Proj>, const T*> constexpr ranges::subrange<I>     find_last( I first, S last, const T& value, Proj proj = {} );			(C++26 起)
		(2)
template< ranges::forward_range R,           class T,           class Proj = std::identity > requires std::indirect_binary_predicate              <ranges::equal_to,               std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_subrange_t<R>     find_last( R&& r, const T& value, Proj proj = {} );				(C++23 起) （直到 C++26）
template< ranges::forward_range R,           class Proj = std::identity,           class T = std::projected_value_t<iterator_t<R>, Proj> > requires std::indirect_binary_predicate              <ranges::equal_to,               std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_subrange_t<R>     find_last( R&& r, const T& value, Proj proj = {} );				(C++26 起)
template< std::forward_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I>     find_last_if( I first, S last, Pred pred, Proj proj = {} );			(3)	(C++23 起)
template< ranges::forward_range R,           class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_subrange_t<R>     find_last_if( R&& r, Pred pred, Proj proj = {} );			(4)	(C++23 起)
template< std::forward_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I>     find_last_if_not( I first, S last, Pred pred, Proj proj = {} );			(5)	(C++23 起)
template< ranges::forward_range R,           class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_subrange_t<R>     find_last_if_not( R&& r, Pred pred, Proj proj = {} );			(6)	(C++23 起)

返回範圍 [first, last) 中滿足特定條件的最後一個元素。

1) find_last 搜尋等於 value 的元素。

3) find_last_if 在範圍 [first, last) 中搜索謂詞 pred 返回 true 的最後一個元素。

5) find_last_if_not 在範圍 [first, last) 中搜索謂詞 pred 返回 false 的最後一個元素。

2,4,6) 與 (1,3,5) 相同，但使用 r 作為源範圍，如同使用 ranges::begin(r) 作為 first 且使用 ranges::end(r) 作為 last。

本頁描述的類函式實體是 演算法函式物件（非正式地稱為 niebloids），即

• 呼叫它們中的任何一個時，不能指定顯式模板引數列表。
• 它們中的任何一個都對 引數依賴查詢 不可見。
• 當這些函式透過函式呼叫運算子左側的名稱進行普通非限定查詢時，會抑制實參依賴查詢。

引數

first, last	-	定義要檢查的元素 範圍 的迭代器-哨兵對
r	-	要檢查的元素範圍
value	-	用於比較元素的數值
pred	-	應用於投影元素的謂詞
proj	-	應用於元素的投影

返回值

1,3,5) 令 i 為範圍 [first, last) 中使 E 為 true 的最後一個迭代器。

返回 ranges::subrange<I>{i, last}，如果未找到此類迭代器，則返回 ranges::subrange<I>{last, last}。

1) E 為 bool(std::invoke(proj, *i) == value)。

3) E 為 bool(std::invoke(pred, std::invoke(proj, *i)))。

5) E 為 bool(!std::invoke(pred, std::invoke(proj, *i)))。

2,4,6) 與 (1,3,5) 相同，但返回型別為 ranges::borrowed_subrange_t<I>。

複雜度

最多應用謂詞和投影 last - first 次。

註解

如果 I 建模 bidirectional_iterator 或（更好）random_access_iterator，則 ranges::find_last、ranges::find_last_if、ranges::find_last_if_not 在常見實現上具有更好的效率。

特性測試宏	值	標準	特性
__cpp_lib_ranges_find_last	202207L	(C++23)	ranges::find_last, ranges::find_last_if, ranges::find_last_if_not
__cpp_lib_algorithm_default_value_type	202403L	(C++26)	演算法的列表初始化 (1,2)

可能的實現

這些實現僅展示當 I 建模 forward_iterator 時使用的較慢演算法。

find_last (1,2)
struct find_last_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, class T = std::projected_value_t<iterator_t<R>, Proj>> requires std::indirect_binary_predicate <ranges::equal_to, std::projected<I, Proj>, const T*> constexpr ranges::subrange<I> operator()(I first, S last, const T &value, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. std::optional<I> found; for (; first != last; ++first) if (std::invoke(proj, *first) == value) found = first;   if (!found) return {first, first};   return {*found, std::ranges::next(*found, last)}; }   template<ranges::forward_range R, class Proj = std::identity, class T = std::projected_value_t<iterator_t<R>, Proj>> requires std::indirect_binary_predicate <ranges::equal_to, std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, const T &value, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), value, std::ref(proj)); } };   inline constexpr find_last_fn find_last;
find_last_if (3,4)
struct find_last_if_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr ranges::subrange<I> operator()(I first, S last, Pred pred, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. std::optional<I> found; for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first))) found = first;   if (!found) return {first, first};   return {*found, std::ranges::next(*found, last)}; }   template<ranges::forward_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_last_if_fn find_last_if;
find_last_if_not (5,6)
struct find_last_if_not_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr ranges::subrange<I> operator()(I first, S last, Pred pred, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. std::optional<I> found; for (; first != last; ++first) if (!std::invoke(pred, std::invoke(proj, *first))) found = first;   if (!found) return {first, first};   return {*found, std::ranges::next(*found, last)}; }   template<ranges::forward_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_last_if_not_fn find_last_if_not;

示例

執行此程式碼

#include <algorithm>
#include <cassert>
#include <forward_list>
#include <iomanip>
#include <iostream>
#include <string_view>
 
int main()
{
    namespace ranges = std::ranges;
 
    constexpr static auto v = {1, 2, 3, 1, 2, 3, 1, 2};
 
    {
        constexpr auto i1 = ranges::find_last(v.begin(), v.end(), 3);
        constexpr auto i2 = ranges::find_last(v, 3);
        static_assert(ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        constexpr auto i1 = ranges::find_last(v.begin(), v.end(), -3);
        constexpr auto i2 = ranges::find_last(v, -3);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    auto abs = [](int x) { return x < 0 ? -x : x; };
 
    {
        auto pred = [](int x) { return x == 3; };
        constexpr auto i1 = ranges::find_last_if(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = ranges::find_last_if(v, pred, abs);
        static_assert(ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        auto pred = [](int x) { return x == -3; };
        constexpr auto i1 = ranges::find_last_if(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = ranges::find_last_if(v, pred, abs);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    {
        auto pred = [](int x) { return x == 1 or x == 2; };
        constexpr auto i1 = ranges::find_last_if_not(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = ranges::find_last_if_not(v, pred, abs);
        static_assert(ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        auto pred = [](int x) { return x == 1 or x == 2 or x == 3; };
        constexpr auto i1 = ranges::find_last_if_not(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = ranges::find_last_if_not(v, pred, abs);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    using P = std::pair<std::string_view, int>;
    std::forward_list<P> list
    {
        {"one", 1}, {"two", 2}, {"three", 3},
        {"one", 4}, {"two", 5}, {"three", 6},
    };
    auto cmp_one = [](const std::string_view &s) { return s == "one"; };
 
    // find latest element that satisfy the comparator, and projecting pair::first
    const auto subrange = ranges::find_last_if(list, cmp_one, &P::first);
 
    std::cout << "The found element and the tail after it are:\n";
    for (P const& e : subrange)
        std::cout << '{' << std::quoted(e.first) << ", " << e.second << "} ";
    std::cout << '\n';
 
#if __cpp_lib_algorithm_default_value_type
    const auto i3 = ranges::find_last(list, {"three", 3}); // (2) C++26
#else
    const auto i3 = ranges::find_last(list, P{"three", 3}); // (2) C++23
#endif
    assert(i3.begin()->first == "three" && i3.begin()->second == 3);
}

輸出

The found element and the tail after it are:
{"one", 4} {"two", 5} {"three", 6}

參閱

ranges::find_end (C++20)	在特定範圍中尋找最後一次出現的元素序列 (演算法函式物件)
ranges::findranges::find_ifranges::find_if_not (C++20)(C++20)(C++20)	尋找第一個滿足特定條件的元素 (演算法函式物件)
ranges::search (C++20)	搜尋一個範圍的元素首次出現的位置 (演算法函式物件)
ranges::includes (C++20)	如果一個序列是另一個序列的子序列，則返回 true (演算法函式物件)
ranges::binary_search (C++20)	判斷一個元素是否存在於部分有序的範圍中 (演算法函式物件)
ranges::containsranges::contains_subrange (C++23)(C++23)	檢查範圍是否包含給定的元素或子範圍 (演算法函式物件)