std::set_intersection
Defined in header <algorithm>
|
||
template< class InputIt1, class InputIt2, class OutputIt > OutputIt set_intersection( InputIt1 first1, InputIt1 last1, |
(1) | (constexpr since C++20) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 > |
(2) | (since C++17) |
template< class InputIt1, class InputIt2, class OutputIt, class Compare > |
(3) | (constexpr since C++20) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, |
(4) | (since C++17) |
Constructs a sorted range beginning at d_first consisting of elements that are found in both sorted ranges [
first1,
last1)
and [
first2,
last2)
.
If [
first1,
last1)
contains m elements that are equivalent to each other and [
first2,
last2)
contains n elements that are equivalent to them, the first std::min(m, n) elements will be copied from [
first1,
last1)
to the output range, preserving order.
[
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) |
If the output range overlaps with [
first1,
last1)
or [
first2,
last2)
, the behavior is undefined.
Contents |
[edit] Parameters
first1, last1 | - | the first range of elements to examine |
first2, last2 | - | the second range of elements to examine |
d_first | - | the beginning of the output range |
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.
| ||
-OutputIt must meet the requirements of LegacyOutputIterator.
| ||
-ForwardIt1, ForwardIt2, ForwardIt3 must meet the requirements of LegacyForwardIterator.
| ||
-Compare must meet the requirements of Compare.
|
[edit] Return value
Iterator past the end of the constructed range.
[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
set_intersection (1) |
---|
template<class InputIt1, class InputIt2, class OutputIt> OutputIt set_intersection(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first) { while (first1 != last1 && first2 != last2) { if (*first1 < *first2) ++first1; else { if (!(*first2 < *first1)) *d_first++ = *first1++; // *first1 and *first2 are equivalent. ++first2; } } return d_first; } |
set_intersection (3) |
template<class InputIt1, class InputIt2, class OutputIt, class Compare> OutputIt set_intersection(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first, Compare comp) { while (first1 != last1 && first2 != last2) { if (comp(*first1, *first2)) ++first1; else { if (!comp(*first2, *first1)) *d_first++ = *first1++; // *first1 and *first2 are equivalent. ++first2; } } return d_first; } |
[edit] Example
#include <algorithm> #include <iostream> #include <iterator> #include <vector> int main() { std::vector<int> v1{7, 2, 3, 4, 5, 6, 7, 8}; std::vector<int> v2{5, 7, 9, 7}; std::sort(v1.begin(), v1.end()); std::sort(v2.begin(), v2.end()); std::vector<int> v_intersection; std::set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(v_intersection)); for (int n : v_intersection) std::cout << n << ' '; std::cout << '\n'; }
Output:
5 7 7
[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 |
---|---|---|---|
LWG 291 | C++98 | it was unspecified how to handle equivalent elements in the input ranges | specified |
[edit] See also
computes the union of two sets (function template) | |
(C++20) |
computes the intersection of two sets (niebloid) |