std::stable_partition

 

C++

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Feature test macros (C++20)

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Symbols index

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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 BidirIt, class UnaryPred > BidirIt stable_partition( BidirIt first, BidirIt last, UnaryPred p );	(1)	(constexpr since C++26)
template< class ExecutionPolicy, class BidirIt, class UnaryPred > BidirIt stable_partition( ExecutionPolicy&& policy,                           BidirIt first, BidirIt last, UnaryPred p );	(2)	(since C++17)

1) Reorders the elements in the range [first, last) in such a way that all elements for which the predicate p returns true precede the elements for which predicate p returns false. Relative order of the elements is preserved.

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)

If any of the following conditions is satisfied, the behavior is undefined:

The type of *first is not Swappable.	(until C++11)
BidirIt is not ValueSwappable. The type of *first is not MoveConstructible. The type of *first is not MoveAssignable.	(since C++11)

Parameters

first, last	-	the range of elements to reorder
policy	-	the execution policy to use
p	-	unary predicate which returns ​true if the element should be ordered before other elements. 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 BidirIt, 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
- BidirIt must meet the requirements of LegacyBidirectionalIterator.
- UnaryPred must meet the requirements of Predicate.

Return value

Iterator to the first element of the second group.

Complexity

Given \(\scriptsize N\)N as std::distance(first, last):

1) Exactly \(\scriptsize N\)N applications of p.

\(\scriptsize O(N)\)O(N) swaps if there is enough extra memory, otherwise at most \(\scriptsize N \cdot log_{2}(N)\)N⋅log2(N) swaps.

2) \(\scriptsize O(N)\)O(N) applications of p.

\(\scriptsize N \cdot log(N)\)N⋅log(N) swaps.

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.

Notes

This function attempts to allocate a temporary buffer. If the allocation fails, the less efficient algorithm is chosen.

Implementations in libc++ and libstdc++ also accept ranges denoted by LegacyForwardIterators as an extension.

Feature-test macro	Value	Std	Feature
__cpp_lib_constexpr_algorithms	202306L	(C++26)	constexpr stable sorting (1)

Example

Run this code

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{0, 0, 3, -1, 2, 4, 5, 0, 7};
    std::stable_partition(v.begin(), v.end(), [](int n) { return n > 0; });
    for (int n : v)
        std::cout << n << ' ';
    std::cout << '\n';
}

Output:

3 2 4 5 7 0 0 -1 0

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2150	C++98	std::stable_partition was only required to place one element satisfying p before one element not satisfying p	corrected the requirement

See also

partition	divides a range of elements into two groups (function template)
ranges::stable_partition (C++20)	divides elements into two groups while preserving their relative order (algorithm function object)