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std::ranges::sort

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
(C++11)
(C++11)
(C++17)

 
Constrained algorithms
All names in this menu belong to namespace std::ranges
       
       
    
     
         
       
       
(C++23)
(C++23)  
(C++23)
(C++23)  
(C++23)            
 
Defined in header <algorithm>
Call signature
template< std::random_access_iterator I, std::sentinel_for <I> S,

          class Comp = ranges::less, class Proj = std::identity >
requires std::sortable <I, Comp, Proj>
constexpr I

    sort( I first, S last, Comp comp = {}, Proj proj = {} );
(1) (since C++20)
template< ranges::random_access_range R, class Comp = ranges::less,

          class Proj = std::identity >
requires std::sortable <ranges::iterator_t <R>, Comp, Proj>
constexpr ranges::borrowed_iterator_t <R>

    sort( R&& r, Comp comp = {}, Proj proj = {} );
(2) (since C++20)

Sorts the elements in the range [firstlast) in non-descending order. The order of equivalent elements is not guaranteed to be preserved.

A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, std::invoke (comp, std::invoke (proj, *(it + n)), std::invoke (proj, *it)) evaluates to false.

1) Elements are compared using the given binary comparison function comp.
2) Same as (1), but uses r as the source range, as if using ranges::begin (r) as first and ranges::end (r) as last.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

[edit] Parameters

first, last - the iterator-sentinel pair defining the range of elements to sort
r - the range to sort
comp - comparison to apply to the projected elements
proj - projection to apply to the elements

[edit] Return value

An iterator equal to last.

[edit] Complexity

\(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)O(N·log(N)) comparisons and projections, where N = ranges::distance (first, last).

[edit] Possible implementation

Note that typical implementations use Introsort. See also the implementation in MSVC STL and libstdc++.

struct sort_fn
{
 template<std::random_access_iterator I, std::sentinel_for <I> S,
 class Comp = ranges::less, class Proj = std::identity >
 requires std::sortable <I, Comp, Proj>
 constexpr I
 operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
 {
 if (first == last)
 return first;
 
 I last_iter = ranges::next (first, last);
 ranges::make_heap (first, last_iter, std::ref (comp), std::ref (proj));
 ranges::sort_heap (first, last_iter, std::ref (comp), std::ref (proj));
 
 return last_iter;
 }
 
 template<ranges::random_access_range R, class Comp = ranges::less,
 class Proj = std::identity >
 requires std::sortable <ranges::iterator_t <R>, Comp, Proj>
 constexpr ranges::borrowed_iterator_t <R>
 operator()(R&& r, Comp comp = {}, Proj proj = {}) const
 {
 return (*this)(ranges::begin (r), ranges::end (r), std::move(comp), std::move(proj));
 }
};
 
inline constexpr sort_fn sort {};

[edit] Notes

std::sort uses std::iter_swap to swap elements, whereas ranges::sort instead uses ranges::iter_swap (which performs ADL for iter_swap, unlike std::iter_swap )

[edit] Example

Run this code
#include <algorithm>
#include <array>
#include <functional>
#include <iomanip>
#include <iostream>
 
void print(auto comment, auto const& seq, char term = ' ')
{
 for (std::cout << comment << '\n'; auto const& elem : seq)
 std::cout << elem << term;
 std::cout << '\n';
}
 
struct Particle
{
 std::string name; double mass; // MeV
 template<class Os> friend
 Os& operator<<(Os& os, Particle const& p)
 {
 return os << std::left << std::setw (8) << p.name << " : " << p.mass << ' ';
 }
};
 
int main()
{
 std::array s {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
 namespace ranges = std::ranges;
 
 ranges::sort (s);
 print("Sort using the default operator<", s);
 
 ranges::sort (s, ranges::greater ());
 print("Sort using a standard library compare function object", s);
 
 struct
 {
 bool operator()(int a, int b) const { return a < b; }
 } customLess;
 ranges::sort (s.begin(), s.end(), customLess);
 print("Sort using a custom function object", s);
 
 ranges::sort (s, [](int a, int b) { return a > b; });
 print("Sort using a lambda expression", s);
 
 Particle particles[]
 {
 {"Electron", 0.511}, {"Muon", 105.66}, {"Tau", 1776.86},
 {"Positron", 0.511}, {"Proton", 938.27}, {"Neutron", 939.57}
 };
 ranges::sort (particles, {}, &Particle::name);
 print("\nSort by name using a projection", particles, '\n');
 ranges::sort (particles, {}, &Particle::mass);
 print("Sort by mass using a projection", particles, '\n');
}

Output:

Sort using the default operator<
0 1 2 3 4 5 6 7 8 9
Sort using a standard library compare function object
9 8 7 6 5 4 3 2 1 0
Sort using a custom function object
0 1 2 3 4 5 6 7 8 9
Sort using a lambda expression
9 8 7 6 5 4 3 2 1 0
 
Sort by name using a projection
Electron : 0.511
Muon  : 105.66
Neutron  : 939.57
Positron : 0.511
Proton  : 938.27
Tau  : 1776.86
 
Sort by mass using a projection
Electron : 0.511
Positron : 0.511
Muon  : 105.66
Proton  : 938.27
Neutron  : 939.57
Tau  : 1776.86

[edit] See also

sorts the first N elements of a range
(algorithm function object)[edit]
sorts a range of elements while preserving order between equal elements
(algorithm function object)[edit]
divides a range of elements into two groups
(algorithm function object)[edit]
sorts a range into ascending order
(function template) [edit]
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