std::stable_sort

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Algorithm library

Execution policies (C++17)
is_execution_policy	sequentialparpar_vec	sequential_execution_policyparallel_execution_policyparallel_vector_execution_policy
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal lexicographical_compare	findfind_iffind_if_not (C++11) find_end find_first_of	adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy	uninitialized_copy_n	uninitialized_fill	uninitialized_fill_n
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class RandomIt > void stable_sort( RandomIt first, RandomIt last );	(1)
template< class ExecutionPolicy, class RandomIt > void stable_sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last );	(2)	(since C++17)
template< class RandomIt, class Compare > void stable_sort( RandomIt first, RandomIt last, Compare comp );	(3)
template< class ExecutionPolicy, class RandomIt, class Compare > void stable_sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );	(4)	(since C++17)

Sorts the elements in the range [first, last) in ascending order. The order of equal elements is guaranteed to be preserved.

1) Elements are compared using operator<.

3) Elements are compared using the given comparison function comp.

2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last	-	the range of elements to sort
policy	-	the execution policy to use. See execution policy for details.
comp	-	comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following:  bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function object must not modify the objects passed to it. The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
- The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

O(N·log²(N)), where N = std::distance(first, last) applications of cmp. If additional memory is available, then the complexity is O(N·log(N)).

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception,

• if policy is std::parallel_vector_execution_policy, std::terminate is called
• if policy is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.
• if policy is some other type, the behavior is implementation-defined

• If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.

Notes

This function attempts to allocate a temporary buffer equal in size to the sequence to be sorted, typically by calling std::get_temporary_buffer. If the allocation fails, the less efficient algorithm is chosen.

Example

Run this code

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
 
struct Employee {
    Employee(int age, std::string name) : age(age), name(name) { } 
    int age;
    std::string name;  // Does not particpate in comparisons
};
 
bool operator<(const Employee &lhs, const Employee &rhs) {
    return lhs.age < rhs.age;
}
 
int main()
{
    std::vector<Employee> v = { 
        Employee(108, "Zaphod"),
        Employee(32, "Arthur"),
        Employee(108, "Ford"),
    };  
 
    std::stable_sort(v.begin(), v.end());
 
    for (const Employee &e : v) {
        std::cout << e.age << ", " << e.name << '\n';
    }   
}

Output:

32, Arthur
108, Zaphod
108, Ford

See also

partial_sort	sorts the first N elements of a range (function template)
sort	sorts a range into ascending order (function template)
std::experimental::parallel::stable_sort (parallelism TS)	parallelized version of std::stable_sort (function template)