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std::partition_copy(3) C++ Standard Libary std::partition_copy(3) NAME std::partition_copy - std::partition_copy Synopsis Defined in header <algorithm> template< class InputIt, class OutputIt1, class OutputIt2, class UnaryPred > std::pair<OutputIt1, OutputIt2> (since C++11) partition_copy( InputIt first, InputIt last, (1) (const- expr since C++20) OutputIt1 d_first_true, OutputIt2 d_first_false, UnaryPred p ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3, class UnaryPred > std::pair<ForwardIt2, ForwardIt3> partition_copy( ExecutionPolicy&& policy, (2) (since C++17) ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first_true, ForwardIt3 d_first_false, UnaryPred p ); 1) Copies the elements from the range [first, last) to two different ranges depending on the value returned by the predicate p. * The elements that satisfy the predicate p are copied to the range beginning at d_first_true. * The rest of the elements are copied to the range beginning at d_first_false. 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) If *first is not writable to d_first_true or d_first_false, the pro- gram is ill-formed. Among the input range and the two output ranges, if any two ranges overlap, the behavior is undefined. Parameters first, last - the range of elements to copy from d_first_true - the beginning of the output range for the elements that satisfy p d_first_false - the beginning of the output range for the elements that do not satisfy p policy - the execution policy to use. See execution policy for details. unary predicate which returns true if the element should be placed in d_first_true. 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. - OutputIt1, OutputIt2 must meet the requirements of LegacyOutputIter- ator. - ForwardIt1, ForwardIt2, ForwardIt3 must meet the requirements of LegacyForwardIterator. - UnaryPred must meet the requirements of Predicate. Return value A std::pair constructed from the iterator to the end of the d_first_true range and the iterator to the end of the d_first_false range. Complexity Exactly std::distance(first, last) applications of p. For the overload (2), there may be a performance cost if ForwardIt's value type is not CopyConstructible. 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 partition_copy (1) template<class InputIt, class OutputIt1, class OutputIt2, class UnaryPred> constexpr //< since C++20 std::pair<OutputIt1, OutputIt2> partition_copy(InputIt first, InputIt last, OutputIt1 d_first_true, OutputIt2 d_first_false, UnaryPred p) { for (; first != last; ++first) { if (p(*first)) { *d_first_true = *first; ++d_first_true; } else { *d_first_false = *first; ++d_first_false; } } return std::pair<OutputIt1, OutputIt2>(d_first_true, d_first_false); } Example // Run this code #include <algorithm> #include <iostream> #include <utility> void print(auto rem, const auto& v) { for (std::cout << rem; const auto& x : v) std::cout << x << ' '; std::cout << '\n'; } int main() { int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; int true_arr[5] = {0}; int false_arr[5] = {0}; std::partition_copy(std::begin(arr), std::end(arr), std::begin(true_arr), std::begin(false_arr), [](int i) { return 4 < i; }); print("true_arr: ", true_arr); print("false_arr: ", false_arr); } Output: true_arr: 5 6 7 8 9 false_arr: 0 1 2 3 4 Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior 1. the value type of InputIt 1. not required P0896R4 C++11 (C++11)/ForwardIt1 (C++17) 2. the behavior is C++17 was required to be CopyAssignable undefined in this 2. the two output ranges could overlap case See also partition divides a range of elements into two groups (function template) divides elements into two groups while pre- serving their stable_partition relative order (function template) copy copies a range of elements to a new location copy_if (function template) (C++11) remove_copy copies a range of elements omitting those that satisfy remove_copy_if specific criteria (function template) ranges::partition_copy copies a range dividing the elements into two groups (C++20) (niebloid) http://cppreference.com 2024.06.10 std::partition_copy(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Possible implementation | Example | Output: | See also
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