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std::is_partitioned(3) C++ Standard Libary std::is_partitioned(3) NAME std::is_partitioned - std::is_partitioned Synopsis Defined in header <algorithm> template< class InputIt, class UnaryPred > (since C++11) bool is_partitioned( InputIt first, InputIt last, (1) (const- expr since C++20) UnaryPred p ); template< class ExecutionPolicy, class ForwardIt, class UnaryPred > bool is_partitioned( ExecutionPolicy&& policy, (2) (since C++17) ForwardIt first, ForwardIt last, UnaryPred p ); 1) Checks whether [first, last) is partitioned by the predicate p: all elements satisfy p appear before all elements that do not. 2) Same as (1), but executed according to policy. This overload participates in overload resolution only if 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) Parameters first, last - the range of elements to check policy - the execution policy to use. See execution policy for details. unary predicate which returns true for the elements expected to be found in the beginning of the range. The expression p(v) must be convertible to bool for every argument v p - 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). Type requirements - 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. Return value true if the elements e of [first, last) are partitioned with respect to the expression p(e). false otherwise. Complexity At most std::distance(first, last) applications of p. 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 ExecutionPolicy is one of the standard policies, std::termi- nate is called. For any other ExecutionPolicy, the behavior is implementation- defined. * If the algorithm fails to allocate memory, std::bad_alloc is thrown. 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; } Example // Run this code #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 See also partition divides a range of elements into two groups (function template) partition_point locates the partition point of a partitioned range (C++11) (function template) ranges::is_partitioned determines if the range is partitioned by the given predicate (C++20) (niebloid) http://cppreference.com 2024.06.10 std::is_partitioned(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | Example | Output: | See also
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