Defined in header <algorithm> | ||
---|---|---|
Call signature | ||
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 = {} ); | (1) | (since C++20) |
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 = {} ); | (2) | (since C++20) |
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) | (since C++20) |
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) | (since C++20) |
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) | (since C++20) |
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) | (since C++20) |
Returns the first element in the range [
first
,
last
)
that satisfies specific criteria:
find
searches for an element equal to value
.find_if
searches for an element for which predicate pred
returns true
.find_if_not
searches for an element 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 |
Iterator to the first element satisfying the condition or iterator equal to last
if no such element is found.
At most last - first
applications of the predicate and projection.
find |
---|
struct find_fn { 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 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; |
#include <algorithm> #include <iostream> #include <iterator> int main() { namespace ranges = std::ranges; 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"; }
Output:
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
(C++20) | finds the first two adjacent items that are equal (or satisfy a given predicate) (niebloid) |
(C++20) | finds the last sequence of elements in a certain range (niebloid) |
(C++20) | searches for any one of a set of elements (niebloid) |
(C++20) | finds the first position where two ranges differ (niebloid) |
(C++20) | searches for a range of elements (niebloid) |
(C++11) | finds the first element satisfying specific criteria (function template) |
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