table of contents
std::stable_partition(3)  C++ Standard Libary  std::stable_partition(3) 
NAME¶
std::stable_partition  std::stable_partition
Synopsis¶
Defined in header <algorithm>
template< class BidirIt, class UnaryPred >
BidirIt stable_partition( BidirIt first, BidirIt last, (1) (constexpr
since C++26)
UnaryPred p );
template< class ExecutionPolicy, class BidirIt, class
UnaryPred >
BidirIt stable_partition( ExecutionPolicy&& policy, (2)
(since C++17)
BidirIt first, BidirIt last,
UnaryPred p );
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
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. (since C++11)
* The type of *first is not MoveAssignable.
Parameters¶
first, last  the range of elements to reorder
policy  the execution policy to use. See execution policy for details.
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
p  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⋅log
2(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 implementationdefined.
* 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.
Featuretest macro Value Std Feature
__cpp_lib_constexpr_algorithms 202306L constexpr stable sorting
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 behaviorchanging defect reports were applied retroactively to
previously published C++ standards.
DR Applied to Behavior as published Correct behavior
std::stable_partition was only required to
LWG 2150 C++98 place one corrected the
element satisfying p before one element not requirement
satisfying p
See also¶
partition divides a range of elements into two groups
(function template)
ranges::stable_partition divides elements into two groups while preserving
their
(C++20) relative order
(niebloid)
2024.06.10  http://cppreference.com 