std::ranges::find,std::ranges::find_if,std::ranges::find_if_not
定义在头文件 <algorithm> 中 |
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调用签名 |
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(1) | ||
template< std::input_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity > |
(自 C++20 起) (直到 C++26) |
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template< std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, |
(自 C++26 起) | |
(2) | ||
template< ranges::input_range R, class T, class Proj = std::identity > requires std::indirect_binary_predicate |
(自 C++20 起) (直到 C++26) |
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template< ranges::input_range R, class Proj = std::identity, 类 T = std::projected_value_t<ranges::iterator_t<R>, Proj> > |
(自 C++26 起) | |
模板< std::input_iterator I, std::sentinel_for<I> S, 类 Proj = std::identity, |
(3) | (自 C++20 起) |
template< ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate |
(4) | (自 C++20 起) |
模板< std::input_iterator I, std::sentinel_for<I> S, 类 Proj = std::identity, |
(5) | (自 C++20 起) |
template< ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate |
(6) | (自 C++20 起) |
返回范围 [
first,
last)
中第一个满足特定条件的元素。
find
搜索与 value 相等的元素。find_if
搜索谓词 pred 返回 true 的元素。find_if_not
搜索谓词 pred 返回 false 的元素。此页面上描述的函数式实体是 niebloid,即
实际上,它们可能作为函数对象实现,或者使用特殊的编译器扩展。
内容 |
[编辑] 参数
first, last | - | 要检查的元素范围。 |
r | - | 要检查的元素范围。 |
value | - | 与元素进行比较的值。 |
pred | - | 应用于投影元素的谓词。 |
proj | - | 应用于元素的投影。 |
[编辑] 返回值
指向第一个满足条件的元素的迭代器,或者如果未找到这样的元素,则指向等于 last 的迭代器。
[编辑] 复杂度
最多 last - first 次谓词和投影应用。
[编辑] 可能的实现
find |
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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 |
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 |
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; |
[编辑] 说明
特性测试 宏 | 值 | Std | 特性 |
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__cpp_lib_algorithm_default_value_type |
202403 | (C++26) | 算法的 列表初始化 (1,2) |
[编辑] 示例
#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()); }
输出
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
[编辑] 另请参阅
(C++20) |
查找第一个相等的两个相邻项目(或满足给定谓词的项目)。 (niebloid) |
(C++20) |
查找给定范围中的最后一个元素序列。 (niebloid) |
(C++20) |
搜索一组元素中的任何一个。 (niebloid) |
(C++20) |
查找两个范围不同的第一个位置。 (niebloid) |
(C++20) |
搜索一组元素的第一个出现位置。 (niebloid) |
(C++11) |
查找第一个满足特定条件的元素。 (函数模板) |