std::ranges::find, std::ranges::find_if, std::ranges::find_if_not

 

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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::input_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 I find( I first, S last, const T& value, Proj proj = {} );			(C++20 起) （直到 C++26）
template< std::input_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 I find( I first, S last, const T& value, Proj proj = {} );			(C++26 起)
		(2)
template< ranges::input_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_iterator_t<R>     find( R&& r, const T& value, Proj proj = {} );				(C++20 起) （直到 C++26）
template< ranges::input_range R, class Proj = std::identity,           class T = std::projected_value_t<ranges::iterator_t<R>, Proj> > requires std::indirect_binary_predicate              <ranges::equal_to,               std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_iterator_t<R>     find( R&& r, const T& value, Proj proj = {} );				(C++26 起)
template< std::input_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr I find_if( I first, S last, Pred pred, Proj proj = {} );			(3)	(C++20 起)
template< ranges::input_range R, class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_iterator_t<R>     find_if( R&& r, Pred pred, Proj proj = {} );			(4)	(C++20 起)
template< std::input_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr I find_if_not( I first, S last, Pred pred, Proj proj = {} );			(5)	(C++20 起)
template< ranges::input_range R, class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_iterator_t<R>     find_if_not( R&& r, Pred pred, Proj proj = {} );			(6)	(C++20 起)

返回範圍 [first, last) 中滿足特定條件的第一個元素。

1) find 搜尋等於 value 的元素。

3) find_if 搜尋謂詞 pred 返回 true 的元素。

5) find_if_not 搜尋謂詞 pred 返回 false 的元素。

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，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。
• 當函式呼叫運算子左側的名稱透過普通非限定查詢找到時，實參依賴查詢被抑制。

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

指向滿足條件的第一個元素的迭代器，如果未找到此類元素，則為等於 last 的迭代器。

複雜度

最多應用謂詞和投影 last - first 次。

可能的實現

find (1)
struct find_fn { template<std::input_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 I operator()(I first, S last, const T& value, Proj proj = {}) const { for (; first != last; ++first) if (std::invoke(proj, *first) == value) return first; return first; }   template<ranges::input_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_iterator_t<R> operator()(R&& r, const T& value, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), value, std::ref(proj)); } };   inline constexpr find_fn find;
find_if (3)
struct find_if_fn { template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr I operator()(I first, S last, Pred pred, Proj proj = {}) const { for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first))) return first; return first; }   template<ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_if_fn find_if;
find_if_not (5)
struct find_if_not_fn { template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr I operator()(I first, S last, Pred pred, Proj proj = {}) const { for (; first != last; ++first) if (!std::invoke(pred, std::invoke(proj, *first))) return first; return first; }   template<ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_if_not_fn find_if_not;

注意

特性測試宏	值	標準	特性
__cpp_lib_algorithm_default_value_type	202403	(C++26)	演算法的列表初始化 (1,2)

示例

執行此程式碼

#include <algorithm>
#include <cassert>
#include <complex>
#include <format>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
 
void projector_example()
{
    struct folk_info
    {
        unsigned uid;
        std::string name, position;
    };
 
    std::vector<folk_info> folks
    {
        {0, "Ana", "dev"},
        {1, "Bob", "devops"},
        {2, "Eve", "ops"}
    };
 
    const auto who{"Eve"};
    if (auto it = std::ranges::find(folks, who, &folk_info::name); it != folks.end())
        std::cout << std::format("Profile:\n"
                                 "    UID: {}\n"
                                 "    Name: {}\n"
                                 "    Position: {}\n\n",
                                 it->uid, it->name, it->position);
}
 
int main()
{
    namespace ranges = std::ranges;
 
    projector_example();
 
    const int n1 = 3;
    const int n2 = 5;
    const auto v = {4, 1, 3, 2};
 
    if (ranges::find(v, n1) != v.end())
        std::cout << "v contains: " << n1 << '\n';
    else
        std::cout << "v does not contain: " << n1 << '\n';
 
    if (ranges::find(v.begin(), v.end(), n2) != v.end())
        std::cout << "v contains: " << n2 << '\n';
    else
        std::cout << "v does not contain: " << n2 << '\n';
 
    auto is_even = [](int x) { return x % 2 == 0; };
 
    if (auto result = ranges::find_if(v.begin(), v.end(), is_even); result != v.end())
        std::cout << "First even element in v: " << *result << '\n';
    else
        std::cout << "No even elements in v\n";
 
    if (auto result = ranges::find_if_not(v, is_even); result != v.end())
        std::cout << "First odd element in v: " << *result << '\n';
    else
        std::cout << "No odd elements in v\n";
 
    auto divides_13 = [](int x) { return x % 13 == 0; };
 
    if (auto result = ranges::find_if(v, divides_13); result != v.end())
        std::cout << "First element divisible by 13 in v: " << *result << '\n';
    else
        std::cout << "No elements in v are divisible by 13\n";
 
    if (auto result = ranges::find_if_not(v.begin(), v.end(), divides_13);
        result != v.end())
        std::cout << "First element indivisible by 13 in v: " << *result << '\n';
    else
        std::cout << "All elements in v are divisible by 13\n";
 
    std::vector<std::complex<double>> nums{{4, 2}};
    #ifdef __cpp_lib_algorithm_default_value_type
        // T gets deduced in (2) making list-initialization possible
        const auto it = ranges::find(nums, {4, 2});
    #else
        const auto it = ranges::find(nums, std::complex<double>{4, 2});
    #endif
    assert(it == nums.begin());
}

輸出

Profile:
    UID: 2
    Name: Eve
    Position: ops
 
v contains: 3
v does not contain: 5
First even element in v: 4
First odd element in v: 1
No elements in v are divisible by 13
First element indivisible by 13 in v: 4

參閱

ranges::adjacent_find (C++20)	尋找第一對相等的（或滿足給定謂詞的）相鄰項 (演算法函式物件)
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::find_first_of (C++20)	搜尋一組元素中的任何一個 (演算法函式物件)
ranges::mismatch (C++20)	尋找兩個範圍開始不同的第一個位置 (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)
findfind_iffind_if_not (C++11)	尋找第一個滿足特定條件的元素 (函式模板)