Defined in header <algorithm> | ||
---|---|---|
Call signature | ||
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 = {} ); | (1) | (since C++23) |
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 = {} ); | (2) | (since C++23) |
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) | (since C++23) |
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) | (since C++23) |
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) | (since C++23) |
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) | (since C++23) |
Returns the last element in the range [
first
,
last
)
that satisfies specific criteria:
find_last
searches for an element equal to value
.find_last_if
searches for the last element in the range [
first
,
last
)
for which predicate pred
returns true
.find_last_if_not
searches for the last element in the range [
first
,
last
)
for which predicate pred
returns false
.r
as the source range, as if using ranges::begin(r)
as first
and ranges::end(r)
as last
.The function-like entities described on this page are niebloids, that is:
In practice, they may be implemented as function objects, or with special compiler extensions.
first, last | - | the range of elements to examine |
r | - | the range of the elements to examine |
value | - | value to compare the elements to |
pred | - | predicate to apply to the projected elements |
proj | - | projection to apply to the elements |
i
be the last iterator in the range [
first
,
last
)
for which E
is true
. Returns ranges::subrange<I>{i, last}
, or ranges::subrange<I>{last, last}
if no such iterator is found.At most last - first
applications of the predicate and projection.
ranges::find_last
, ranges::find_last_if
, ranges::find_last_if_not
have better efficiency on common implementations if I
models bidirectional_iterator
or (better) random_access_iterator
.
Feature-test macro | Value | Std | Comment |
---|---|---|---|
__cpp_lib_ranges_find_last | 202207L | (C++23) |
ranges::find_last , ranges::find_last_if , ranges::find_last_if_not |
These implementations only show the slower algorithm used when I
models forward_iterator
.
find_last (1-2) |
---|
struct find_last_fn { 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> 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. I found {}; for (; first != last; ++first) if (std::invoke(proj, *first) == value) found = first; if (found == I {}) return {first, first}; return {found, std::ranges::next(found, last)}; } 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> 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. I found {}; for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first))) found = first; if (found == I {}) 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. I found {}; for (; first != last; ++first) if (!std::invoke(pred, std::invoke(proj, *first))) found = first; if (found == I {}) 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; |
A link to test: Compiler Explorer/g++-trunk.
#include <algorithm> #include <forward_list> #include <iomanip> #include <iostream> #include <string_view> int main() { constexpr static auto v = {1, 2, 3, 1, 2, 3, 1, 2}; { constexpr auto i1 = std::ranges::find_last(v.begin(), v.end(), 3); constexpr auto i2 = std::ranges::find_last(v, 3); static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5); static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5); } { constexpr auto i1 = std::ranges::find_last(v.begin(), v.end(), -3); constexpr auto i2 = std::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 = std::ranges::find_last_if(v.begin(), v.end(), pred, abs); constexpr auto i2 = std::ranges::find_last_if(v, pred, abs); static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5); static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5); } { auto pred = [](int x) { return x == -3; }; constexpr auto i1 = std::ranges::find_last_if(v.begin(), v.end(), pred, abs); constexpr auto i2 = std::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 = std::ranges::find_last_if_not(v.begin(), v.end(), pred, abs); constexpr auto i2 = std::ranges::find_last_if_not(v, pred, abs); static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5); static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5); } { auto pred = [](int x) { return x == 1 or x == 2 or x == 3; }; constexpr auto i1 = std::ranges::find_last_if_not(v.begin(), v.end(), pred, abs); constexpr auto i2 = std::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 = std::ranges::find_last_if(list, cmp_one, &P::first); // print the found element and the "tail" after it for (P const& e : subrange) std::cout << '{' << std::quoted(e.first) << ", " << e.second << "} "; std::cout << '\n'; }
Output:
{"one", 4} {"two", 5} {"three", 6}
(C++20) | finds the last sequence of elements in a certain range (niebloid) |
(C++20)(C++20)(C++20) | finds the first element satisfying specific criteria (niebloid) |
(C++20) | searches for a range of elements (niebloid) |
(C++20) | returns true if one sequence is a subsequence of another (niebloid) |
(C++20) | determines if an element exists in a partially-ordered range (niebloid) |
(C++23)(C++23) | checks if the range contains the given element or subrange (niebloid) |
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