std::stable_sort

Defined in header `<algorithm>`
template< class RandomIt > void stable_sort( RandomIt first, RandomIt last );	(1)
template< class RandomIt, class Compare > void stable_sort( RandomIt first, RandomIt last, Compare comp );	(2)

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.

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

(none)

[edit] Complexity

$O(N\cdotlog 2 (N))$ , where N = std::distance(first, last) applications of cmp. If additional memory is available, then the complexity is $O(N\cdotlog(N))$ .

[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

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

[edit] 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)

Language
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Concepts
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Technical Specifications