std::ranges::find_end
std::ranges
<algorithm>
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>
find_end( I1 first1, S1 last1, I2 first2, S2 last2,
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>
find_end( R1&& r1, R2&& r2, Pred pred = {},
[first2, last2) in the range [first1, last1), after projection with proj1 and proj2 respectively. The projected elements are compared using the binary predicate pred.The function-like entities described on this page are algorithm function objects (informally known as 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.
Contents
[edit] Parameters
[edit] Return value
[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 return value is effectively initialized with {last1, last1}.[edit] Complexity
At most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) applications of the corresponding predicate and each projection, where \(\scriptsize S\)S is ranges::distance (first2, last2) and \(\scriptsize N\)N is ranges::distance (first1, last1) for (1), or \(\scriptsize S\)S is ranges::distance (r2) and \(\scriptsize N\)N is ranges::distance (r1) for (2).
[edit] 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 however does not change the theoretical complexity of the worst case.
[edit] 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 {};
[edit] 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) ^^^^^
[edit] See also
(algorithm function object)[edit]
(algorithm function object)[edit]
(algorithm function object)[edit]
(algorithm function object)[edit]