< cpp‎ | algorithm
Defined in header <algorithm>
template< class RandomIt >
void stable_sort( RandomIt first, RandomIt last );
template< class RandomIt, class Compare >
void stable_sort( RandomIt first, RandomIt last, Compare comp );

Sorts the elements in the range [first, last) in ascending order. The order of equal elements is guaranteed to be preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.


[edit] Parameters

first, last - the range of elements to sort
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.

[edit] Return value


[edit] 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)).

[edit] 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.

[edit] Example

#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 << ", " << << '\n';


32, Arthur
108, Zaphod
108, Ford

[edit] See also

sorts the first N elements of a range
(function template)
sorts a range into ascending order
(function template)
parallelized version of std::stable_sort
(function template)