std::is_partitioned
<algorithm>
bool is_partitioned( InputIt first, InputIt last, UnaryPred p );
(constexpr since C++20)
bool is_partitioned( ExecutionPolicy&& policy,
[first, last) is partitioned by the predicate p: all elements satisfy p appear before all elements that do not.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
The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed, nor is VT unless for VT a move is equivalent to a copy(since C++11).
InputIt must meet the requirements of LegacyInputIterator.
ForwardIt must meet the requirements of LegacyForwardIterator. and its value type must be convertible to UnaryPred's parameter type.
UnaryPred must meet the requirements of Predicate.
[edit] Return value
true if the elements e of [first, last) are partitioned with respect to the expression p(e). false otherwise.
[edit] Complexity
At most std::distance (first, last) applications of p.
[edit] Exceptions
The overload with a template parameter named ExecutionPolicy reports errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicyis 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
template<class InputIt, class UnaryPred> bool is_partitioned(InputIt first, InputIt last, UnaryPred p) { for (; first != last; ++first) if (!p(*first)) break; for (; first != last; ++first) if (p(*first)) return false; return true; }
[edit] Example
#include <algorithm> #include <array> #include <iostream> int main() { std::array <int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9}; auto is_even = [](int i) { return i % 2 == 0; }; std::cout.setf(std::ios_base::boolalpha ); std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' '; std::partition (v.begin(), v.end(), is_even); std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' '; std::reverse (v.begin(), v.end()); std::cout << std::is_partitioned(v.cbegin(), v.cend(), is_even) << ' '; std::cout << std::is_partitioned(v.crbegin(), v.crend(), is_even) << '\n'; }
Output:
false true false true
[edit] See also
(algorithm function object)[edit]