std::ranges:: find, std::ranges:: find_if, std::ranges:: find_if_not
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定义于头文件
<algorithm>
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调用签名
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| (1) | ||
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template
<
std::
input_iterator
I,
std::
sentinel_for
<
I
>
S,
class
T,
class
Proj
=
std::
identity
>
|
(C++20 起)
(C++26 前) |
|
|
template
<
std::
input_iterator
I,
std::
sentinel_for
<
I
>
S,
class
Proj
=
std::
identity
,
|
(C++26 起) | |
| (2) | ||
|
template
<
ranges::
input_range
R,
class
T,
class
Proj
=
std::
identity
>
requires
std::
indirect_binary_predicate
|
(C++20 起)
(C++26 前) |
|
|
template
<
ranges::
input_range
R,
class
Proj
=
std::
identity
,
class
T
=
std
::
projected_value_t
<
ranges::
iterator_t
<
R
>
, Proj
>
>
|
(C++26 起) | |
| (3) | ||
|
template
<
std::
input_iterator
I,
std::
sentinel_for
<
I
>
S,
class
Proj
=
std::
identity
,
|
(3) | (C++20 起) |
|
template
<
ranges::
input_range
R,
class
Proj
=
std::
identity
,
std::
indirect_unary_predicate
|
返回范围
[
first
,
last
)
中首个满足特定条件的元素：
find
搜索与
value
相等的元素。
find_if
搜索使谓词
pred
返回
true
的元素。
find_if_not
查找使谓词
pred
返回
false
的元素。
本页面描述的函数式实体是 算法函数对象 （非正式称为 niebloids ），即：
目录 |
参数
| first, last | - | 定义待检验元素范围的 区间 的迭代器-哨位对 |
| r | - | 待检验元素的范围 |
| value | - | 用于与元素比较的值 |
| pred | - | 应用于投影元素的谓词 |
| proj | - | 应用于元素的投影 |
返回值
指向首个满足条件的元素的迭代器，若找不到此类元素则返回等于 last 的迭代器。
复杂度
最多 last - first 次谓词和投影函数的应用。
可能的实现
| 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 |
注释
| 功能测试 宏 | 值 | 标准 | 功能 |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type
|
202403
|
(C++26) | 列表初始化 用于算法 ( 1,2 ) |
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: " << 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<span class
参见
|
(C++20)
|
查找首个相邻的相等元素（或满足给定谓词的元素对）
(算法函数对象) |
|
(C++20)
|
在特定范围内查找最后出现的元素序列
(算法函数对象) |
|
(C++20)
|
搜索一组元素中的任意一个元素
(算法函数对象) |
|
(C++20)
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查找两个范围首次出现差异的位置
(算法函数对象) |
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(C++20)
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搜索元素范围的首次出现
(算法函数对象) |
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(C++11)
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查找首个满足特定条件的元素
(函数模板) |