Defined in header <algorithm>
template< class BidirIt, class UnaryPredicate >
BidirIt stable_partition( BidirIt first, BidirIt last, UnaryPredicate p );
template< class ExecutionPolicy, class BidirIt, class UnaryPredicate >
BidirIt stable_partition( ExecutionPolicy&& policy, BidirIt first, BidirIt last, UnaryPredicate 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 only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.


first, last - the range of elements to reorder
policy - the execution policy to use. See execution policy for details.
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 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.


Given N = last - first.

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


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.


#include <iostream>
#include <algorithm>
#include <vector>
int main()
    std::vector<int> v{0, 0, 3, 0, 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';


3 2 4 5 7 0 0 0 0

See also

divides a range of elements into two groups
(function template)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.