std::is_partitioned

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges(C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
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)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

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

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 all following conditions are satisfied:

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 pair of iterators defining the range of elements to examine
policy	-	the execution policy to use
p	-	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 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::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 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))returnfalse;returntrue;}

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 (C++11)	locates the partition point of a partitioned range (function template)
ranges::is_partitioned (C++20)	determines if the range is partitioned by the given predicate (algorithm function object)