NAME¶

std::stable_partition - std::stable_partition

Synopsis¶

Defined in header <algorithm>
template< class BidirIt, class UnaryPredicate >
BidirIt stable_partition( BidirIt first, BidirIt last, (1)
UnaryPredicate p );
template< class ExecutionPolicy, class BidirIt, class
UnaryPredicate > (2) (since C++17)
BidirIt stable_partition( ExecutionPolicy&& policy, BidirIt first,
BidirIt last, UnaryPredicate 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 does not participate
in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

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 ValueSwappable and
LegacyBidirectionalIterator.
-
The type of dereferenced BidirIt must meet the requirements of MoveAssignable and
MoveConstructible.
-
UnaryPredicate must meet the requirements of Predicate.

Return value¶

Iterator to the first element of the second group

Complexity¶

Given N = std::distance(first, last),

1) Exactly N applications of the predicate and O(N) swaps if there is enough extra
memory. If memory is insufficient, at most N log N swaps.
2) O(N log N) swaps and O(N) applications of the predicate

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.

Example¶

// Run this code

#include <iostream>
#include <algorithm>
#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

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)