std::includes
Defined in header <algorithm>
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template< class InputIt1, class InputIt2 > bool includes( InputIt1 first1, InputIt1 last1, |
(1) | (constexpr since C++20) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > |
(2) | (since C++17) |
template< class InputIt1, class InputIt2, class Compare > bool includes( InputIt1 first1, InputIt1 last1, |
(3) | (constexpr since C++20) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class Compare > |
(4) | (since C++17) |
Returns true if the sorted range [
first2,
last2)
is a subsequence of the sorted range [
first1,
last1)
(a subsequence need not be contiguous).
[
first1,
last1)
or [
first2,
last2)
is not sorted with respect to operator<(until C++20)std::less{}(since C++20), the behavior is undefined.[
first1,
last1)
or [
first2,
last2)
is not sorted with respect to comp, the behavior is undefined.
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
Contents |
[edit] Parameters
first1, last1 | - | the sorted range of elements to examine |
first2, last2 | - | the sorted range of elements to search for |
policy | - | the execution policy to use. See execution policy for details. |
comp | - | comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) |
Type requirements | ||
-InputIt1, InputIt2 must meet the requirements of LegacyInputIterator.
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-ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
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-Compare must meet the requirements of Compare.
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[edit] Return value
true if [
first2,
last2)
is a subsequence of [
first1,
last1)
; otherwise false.
An empty sequence is a subsequence of any sequence, so true is returned if [
first2,
last2)
is empty.
[edit] Complexity
Given N
1 as std::distance(first1, last1) and N
2 as std::distance(first2, last2):
1+N
2)-1 applications of the comparison function comp.
[edit] Exceptions
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Possible implementation
include (1) |
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template<class InputIt1, class InputIt2> bool includes(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2) { for (; first2 != last2; ++first1) { if (first1 == last1 || *first2 < *first1) return false; if (!(*first1 < *first2)) ++first2; } return true; } |
include (3) |
template<class InputIt1, class InputIt2, class Compare> bool includes(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Compare comp) { for (; first2 != last2; ++first1) { if (first1 == last1 || comp(*first2, *first1)) return false; if (!comp(*first1, *first2)) ++first2; } return true; } |
[edit] Example
#include <algorithm> #include <cctype> #include <iostream> template<class Os, class Co> Os& operator<<(Os& os, const Co& v) { for (const auto& i : v) os << i << ' '; return os << '\t'; } int main() { const auto v1 = {'a', 'b', 'c', 'f', 'h', 'x'}, v2 = {'a', 'b', 'c'}, v3 = {'a', 'c'}, v4 = {'a', 'a', 'b'}, v5 = {'g'}, v6 = {'a', 'c', 'g'}, v7 = {'A', 'B', 'C'}; auto no_case = [](char a, char b) { return std::tolower(a) < std::tolower(b); }; std::cout << v1 << "\nincludes:\n" << std::boolalpha << v2 << ": " << std::includes(v1.begin(), v1.end(), v2.begin(), v2.end()) << '\n' << v3 << ": " << std::includes(v1.begin(), v1.end(), v3.begin(), v3.end()) << '\n' << v4 << ": " << std::includes(v1.begin(), v1.end(), v4.begin(), v4.end()) << '\n' << v5 << ": " << std::includes(v1.begin(), v1.end(), v5.begin(), v5.end()) << '\n' << v6 << ": " << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end()) << '\n' << v7 << ": " << std::includes(v1.begin(), v1.end(), v7.begin(), v7.end(), no_case) << " (case-insensitive)\n"; }
Output:
a b c f h x includes: a b c : true a c : true a a b : false g : false a c g : false A B C : true (case-insensitive)
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
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LWG 1205 | C++98 | the return value was unclear if [ first2, last2) is empty
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returns true in this case |
[edit] See also
computes the difference between two sets (function template) | |
searches for the first occurrence of a range of elements (function template) | |
(C++20) |
returns true if one sequence is a subsequence of another (niebloid) |