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:
If any of the following conditions is satisfied, the behavior is undefined:
[edit] Parameters
first, last
-
the pair of iterators defining the
range of elements to reorder
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
-
UnaryPred must meet the requirements of
Predicate.
[edit] Return value
Iterator to the first element of the second group.
[edit] 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.
[edit] 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.
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.
[edit] Example
#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:
[edit] 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
|
[edit] See also
divides a range of elements into two groups
(function template) [edit]
divides elements into two groups while preserving their relative order
(algorithm function object)[edit]