std::ranges::search
Defined in header <algorithm> |
||
---|---|---|
Call signature | ||
template< std::forward_iterator I1, std::sentinel_for<I1> S1, std::forward_iterator I2, std::sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity > requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2> constexpr ranges::subrange<I1> search( I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ); |
(1) | (since C++20) |
template< ranges::forward_range R1, ranges::forward_range R2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity> requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, Proj1, Proj2> constexpr ranges::borrowed_subrange_t<R1> search( R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ); |
(2) | (since C++20) |
1) Searches for the
first occurrence of the sequence of elements
[first2, last2)
in the range
[first1, last1)
. Elements are compared using binary predicate
pred
after being projected with
proj2
and
proj1
, respectively.
2) Same as
(1), but uses
r1
as the first source range and
r2
as the second source range, as if using
ranges::begin(r1)
as
first1
,
ranges::end(r1)
as
last1
,
ranges::begin(r2)
as
first2
, and
ranges::end(r2)
as
last2
.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
first1, last1 | - | the range of elements to examine (aka haystack) |
first2, last2 | - | the range of elements to search for (aka needle) |
r1 | - | the range of elements to examine (aka haystack) |
r2 | - | the range of elements to search for (aka needle) |
pred | - | binary predicate to apply to the projected elements |
proj1 | - | projection to apply to the elements in the first range |
proj2 | - | projection to apply to the elements in the second range |
Return value
1) Returns a
ranges::subrange
value that is the first occurrence of the sequence
[first2, last2)
(aka
needle) in the range
[first1, last1)
(aka
haystack), after application of the projections
proj1
and
proj2
to the elements of both sequences respectively with consequencing application of the binary predicate
pred
to compare projected elements.
If no such occurrence is found, ranges::subrange{last1, last1}
is returned. If the range to search for (aka.
first2 == last2
, then the
ranges::subrange{first1, first1}
is returned.
Complexity
At most S*N
applications of the corresponding predicate and each projection, where
(1) S = ranges::distance(first2, last2)
and N = ranges::distance(first1, last1)
;
(2) S = ranges::distance(r2)
and N = ranges::distance(r1)
.
Possible implementation
struct search_fn { template<std::forward_iterator I1, std::sentinel_for<I1> S1, std::forward_iterator I2, std::sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity> requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2> constexpr ranges::subrange<I1> operator()(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { for (;; ++first1) { I1 it1 = first1; for (I2 it2 = first2;; ++it1, ++it2) { if (it2 == last2) return {first1, it1}; if (it1 == last1) return {it1, it1}; if (!std::invoke(pred, std::invoke(proj1, *it1), std::invoke(proj2, *it2))) break; } } } template<ranges::forward_range R1, ranges::forward_range R2, class Pred = ranges::equal_to, class Proj1 = std::identity, class Proj2 = std::identity> requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, Proj1, Proj2> constexpr ranges::borrowed_subrange_t<R1> operator()(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { return (*this)(ranges::begin(r1), ranges::end(r1), ranges::begin(r2), ranges::end(r2), std::move(pred), std::move(proj1), std::move(proj2)); } }; inline constexpr search_fn search{}; |
Example
#include <algorithm> #include <cctype> #include <iostream> #include <iterator> #include <string_view> using namespace std::literals; void print(int id, const auto& haystack, const auto& needle, const auto& found) { std::cout << id << "). search(\"" << haystack << "\", \"" << needle << "\"); "; const auto first = std::distance(haystack.begin(), found.begin()); const auto last = std::distance(haystack.begin(), found.end()); if (found.empty()) { std::cout << "not found;"; } else { std::cout << "found: \""; for (const auto x: found) { std::cout << x; } std::cout << "\";"; } std::cout << " subrange: {" << first << ", " << last << "}\n"; } int main() { constexpr auto haystack {"abcd abcd"sv}; constexpr auto needle {"bcd"sv}; // the search uses iterator pairs begin()/end(): constexpr auto found1 = std::ranges::search( haystack.begin(), haystack.end(), needle.begin(), needle.end()); print(1, haystack, needle, found1); // the search uses ranges r1, r2: constexpr auto found2 = std::ranges::search(haystack, needle); print(2, haystack, needle, found2); // 'needle' range is empty: constexpr auto none {""sv}; constexpr auto found3 = std::ranges::search(haystack, none); print(3, haystack, none, found3); // 'needle' will not be found: constexpr auto awl {"efg"sv}; constexpr auto found4 = std::ranges::search(haystack, awl); print(4, haystack, awl, found4); // the search uses custom comparator and projections: constexpr auto bodkin {"234"sv}; auto found5 = std::ranges::search(haystack, bodkin, [](const int x, const int y) { return x == y; }, // pred [](const int x) { return std::toupper(x); }, // proj1 [](const int y) { return y + 'A' - '1'; } // proj2 ); print(5, haystack, bodkin, found5); }
Output:
1). search("abcd abcd", "bcd"); found: "bcd"; subrange: {1, 4} 2). search("abcd abcd", "bcd"); found: "bcd"; subrange: {1, 4} 3). search("abcd abcd", ""); not found; subrange: {0, 0} 4). search("abcd abcd", "efg"); not found; subrange: {9, 9} 5). search("abcd abcd", "234"); found: "bcd"; subrange: {1, 4}
See also
(C++20)
|
finds the first two adjacent items that are equal (or satisfy a given predicate) (niebloid) |
(C++20)(C++20)(C++20)
|
finds the first element satisfying specific criteria (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)
|
returns true if one sequence is a subsequence of another (niebloid) |
(C++20)
|
finds the first position where two ranges differ (niebloid) |
(C++20)
|
searches for a number consecutive copies of an element in a range (niebloid) |
searches for a range of elements (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/algorithm/ranges/search