std::is_partitioned

C++

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

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Algorithms library

Iterators library

Numerics library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Algorithm library

Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseq	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policy
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17)	uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

Defined in header <algorithm>
	(1)
template< class InputIt, class UnaryPredicate > bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p );			(since C++11) (until C++20)
template< class InputIt, class UnaryPredicate > constexpr bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p );			(since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate > bool is_partitioned( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryPredicate p );		(2)	(since C++17)

1) Returns true if all elements in the range [first, last) that satisfy the predicate p appear before all elements that don't. Also returns true if [first, last) is empty.

2) Same as (1), but executed according to policy. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last	-	the range of elements to check
policy	-	the execution policy to use. See execution policy for details.
p	-	unary predicate which returns true for the elements expected to be found in the beginning of the range. The signature of the predicate function should be equivalent to the following: bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. The type Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type.
Type requirements
- InputIt must meet the requirements of InputIterator.
- ForwardIt must meet the requirements of ForwardIterator. and its value type must be convertible to UnaryPredicate's argument type
- UnaryPredicate must meet the requirements of Predicate.

Return value

true if the range [first, last) is empty or is partitioned by p. 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 three standard policies, std::terminate 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 UnaryPredicate > bool is_partitioned(InputIt first, InputIt last, UnaryPredicate 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.begin(), v.end(), is_even);
}

Output:

false true false

See also

partition	divides a range of elements into two groups (function template)
partition_point (C++11)	locates the partition point of a partitioned range (function template)