std:: stable_partition

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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)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
Modifying sequence operations
Copy operations
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17) (C++11)
(C++20) (C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
stable_partition
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
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

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:

(until C++11)
(since C++11)

Parameters

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 LegacyBidirectionalIterator .
-
UnaryPred must meet the requirements of Predicate .

Return value

Iterator to the first element of the second group.

Complexity

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

1) Exactly N applications of p .
O(N) swaps if there is enough extra memory, otherwise at most N⋅log 2 (N) swaps.
2) O(N) applications of p .
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 LegacyForwardIterator s as an extension.

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

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:

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

divides a range of elements into two groups
(function template)
divides elements into two groups while preserving their relative order
(algorithm function object)