std::ranges::find_end
| Defined in header <algorithm>
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| Call signature |
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| template<std::forward_iterator I1, std::sentinel_for<I1> S1, std::forward_iterator I2, std::sentinel_for<I2> S2, |
(1) | (since C++20) |
| template<ranges::forward_range R1, ranges::forward_range R2, class Pred = ranges::equal_to, |
(2) | (since C++20) |
[first2, last2) in the range [first1, last1), after projection with proj1 and proj2) respectively. The projected elements are compared using the binary predicate pred.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 cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
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 compare the 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
{i, i + (i == last1 ? 0 : last2 - first2)} that is the last occurrence of the sequence [first2, last2) in range [first1, last1) (after projections with proj1 and proj2). If [first2, last2) is empty or if no such sequence is found, the returned object is effectivelly intialized with {last1, last1}.Complexity
At most S*(N-S+1) applications of the corresponding predicate and each projection, where S = last2 - first2 and N = last1 - first1 for (1), or S = ranges::size(r2) and N = ranges::size(r1) for (2).
Notes
An implementation can improve efficiency of the search if the input iterators model std::bidirectional_iterator by searching from the end towards the begin. Modelling the std::random_access_iterator may improve the comparison speed. All this hovewer does not change the theoretical complexity of the worst case.
Possible implementation
struct find_end_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 { if (first2 == last2) { auto last_it = ranges::next(first1, last1); return {last_it, last_it}; } auto result = ranges::search( std::move(first1), last1, first2, last2, pred, proj1, proj2); if (result.empty()) return result; for (;;) { auto new_result = ranges::search( std::next(result.begin()), last1, first2, last2, pred, proj1, proj2); if (new_result.empty()) return result; else result = std::move(new_result); } } 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 find_end_fn find_end{}; |
Example
#include <algorithm> #include <array> #include <cctype> #include <iostream> #include <ranges> #include <string_view> void print(const auto haystack, const auto needle) { const auto pos = std::distance(haystack.begin(), needle.begin()); std::cout << "In \""; for (const auto c : haystack) { std::cout << c; } std::cout << "\" found \""; for (const auto c : needle) { std::cout << c; } std::cout << "\" at position [" << pos << ".." << pos + needle.size() << ")\n" << std::string(4 + pos, ' ') << std::string(needle.size(), '^') << '\n'; } int main() { using namespace std::literals; constexpr auto secret{"password password word..."sv}; constexpr auto wanted{"password"sv}; constexpr auto found1 = std::ranges::find_end( secret.cbegin(), secret.cend(), wanted.cbegin(), wanted.cend()); print(secret, found1); constexpr auto found2 = std::ranges::find_end(secret, "word"sv); print(secret, found2); const auto found3 = std::ranges::find_end(secret, "ORD"sv, [](const char x, const char y) { // uses a binary predicate return std::tolower(x) == std::tolower(y); }); print(secret, found3); const auto found4 = std::ranges::find_end(secret, "SWORD"sv, {}, {}, [](char c) { return std::tolower(c); }); // projects the 2nd range print(secret, found4); static_assert(std::ranges::find_end(secret, "PASS"sv).empty()); // => not found }
Output:
In "password password word..." found "password" at position [9..17)
^^^^^^^^
In "password password word..." found "word" at position [18..22)
^^^^
In "password password word..." found "ord" at position [19..22)
^^^
In "password password word..." found "sword" at position [12..17)
^^^^^See also
| finds the last sequence of elements in a certain range (function template) | |
| (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) |
searches for any one of a set of elements (niebloid) |
| (C++20) |
searches for the first occurrence of a range of elements (niebloid) |
| (C++20) |
searches for the first occurrence of a number consecutive copies of an element in a range (niebloid) |
