std::ranges::find_last, std::ranges::find_last_if, std::ranges::find_last_if_not
来自 zh.cppreference.net
| 定义于头文件 <algorithm>
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| 调用签名 |
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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 = {} );
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(1) | (C++23 起) (C++26 前) |
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 = {} );
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(C++26 起) | |
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 = {} );
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(2) | (C++23 起) (C++26 前) |
template< ranges::forward_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_subrange_t<R>
find_last( R&& r, const T& value, Proj proj = {} );
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(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 = {} );
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(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 = {} );
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(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 = {} );
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(6) | (C++23 起) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_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*>
ranges::subrange<I> find_last( Ep&& policy, I first, S last,
const T& value, Proj proj = {} );
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(7) | (C++26 起) |
template< /*execution-policy*/ Ep, /*sized-random-access-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*>
ranges::borrowed_subrange_t<R>
find_last( Ep&& policy, R&& r, const T& value, Proj proj = {} );
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(8) | (C++26 起) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred >
ranges::subrange<I> find_last_if( Ep&& policy, I first, S last,
Pred pred, Proj proj = {} );
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(9) | (C++26 起) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = std::identity,
std::indirect_unary_predicate
<std::projected<ranges::iterator_t<R>, Proj>> Pred >
ranges::borrowed_subrange_t<R>
find_last_if( Ep&& policy, R&& r, Pred pred, Proj proj = {} );
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(10) | (C++26 起) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred >
ranges::subrange<I> find_last_if_not( Ep&& policy, I first, S last,
Pred pred, Proj proj = {} );
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(11) | (C++26 起) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = std::identity,
std::indirect_unary_predicate
<std::projected<ranges::iterator_t<R>, Proj>> Pred >
ranges::borrowed_subrange_t<R>
find_last_if_not( Ep&& policy, R&& r, Pred pred, Proj proj = {} );
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(12) | (C++26 起) |
关于 /*execution-policy*/ 的定义，见此页面；关于 /*sized-random-access-range*/ 的定义，见此页面。
返回源范围 proj 或 [first, last) 中最后一个（经 r 投射后的）满足特定条件的元素：
1,2)
find_last 搜索最后一个等于 value 的元素。3,4)
find_last_if 搜索最后一个使谓词 pred 返回 true 的元素。5,6)
find_last_if_not 搜索最后一个使谓词 pred 返回 false 的元素。7-12) 与 (1-6) 相同，但按照
policy 执行。此页面上描述的类似函数的实体是算法函数对象（非正式名称为niebloids），即：
参数
| first, last | - | 定义源范围 |
| r的迭代器-哨兵对 | - | 源范围 |
| value | - | 目标值 |
| pred | - | 应用于（投影后）元素的谓词 |
| proj | - | 应用于元素的投影 |
| policy | - | 要使用的执行策略 |
返回值
从满足条件的最后一个元素到源范围末尾的子范围，如果没有找到这样的元素，则为空范围。
复杂度
给定 N 作为 ranges::distance(first, last) 或 ranges::distance(r)：
1,2) 至多 N 次比较和
proj 的应用。3-6) 至多 N 次
pred 和 proj 的应用。7,8) 𝓞(N) 次比较和
proj 的应用。9-12) 𝓞(N) 次
pred 和 proj 的应用。异常
7-12) 在执行过程中：
- 如果并行化所需的临时内存资源不可用，std::bad_alloc 会被抛出。
- 如果通过算法参数访问对象时抛出未捕获的异常，则行为由执行策略决定（对于 标准策略，会调用 std::terminate）。
注释
ranges::find_last
、
ranges::find_last_if
、
ranges::find_last_if_not
在常见实现中具有更高效率，若
I
满足
bidirectional_iterator
或（更优情况下）
random_access_iterator
的概念要求。
| 功能测试 宏 | 值 | 标准 | 功能 |
|---|---|---|---|
__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) | 列表初始化 用于算法 ( 1,2 ) |
可能的实现
这些实现仅展示了当 I 满足 forward_iterator 时使用的较慢算法。
| find_last |
|---|
struct find_last_fn
{
template<std::forward_iterator I, std::sentinel_for<I> S,
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<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, 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)(ranges::begin(r),
ranges::next(ranges::begin(r), ranges::end(r)),
value, std::ref(proj));
}
};
inline constexpr find_last_fn find_last;
|
| find_last_if |
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, 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)(ranges::begin(r),
ranges::next(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 |
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, 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)(ranges::begin(r),
ranges::next(ranges::begin(r), ranges::end(r)),
std::ref(pred), std::ref(proj));
}
};
inline constexpr find_last_if_not_fn find_last_if_not;
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示例
运行此代码
#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 { {"一", 1}, {"two", 2}, {"三", 3}, {"一", 4}, {"two", 5}, {"三", 6}, }; auto cmp_one = [](const std::string_view &s) { return s == "one"; }; // 查找满足比较器的最新元素，并投影 pair::first const auto subrange = ranges::find_last_if(list, cmp_one, &P::first); std::cout << "找到的元素及其后续内容为：\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, {"三", 3}); // (2) C++26 #else const auto i3 = ranges::find_last(list, P{"三", 3}); // (2) C++23 #endif assert(i3.begin()->first == "三" && i3.begin()->second == 3); }
输出：
找到的元素及其后续内容为：
{"one", 4} {"two", 5} {"three", 6}
另见
(C++20) |
查找特定范围中元素的最后出现 （算法函数对象） |
(C++20)(C++20)(C++20) |
查找满足特定条件的第一个元素 （算法函数对象） |
(C++20) |
搜索某一元素范围的首次出现 （算法函数对象） |
(C++20) |
确定一个序列是否为另一个序列的子序列 （算法函数对象） |
(C++20) |
使用二分搜索确定元素是否存在于范围中 （算法函数对象） |
(C++23)(C++23) |
检查范围是否包含给定元素或子范围 （算法函数对象） |