std::ranges::sort
| Defined in header <algorithm>
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| Call signature |
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| template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > |
(1) | (since C++20) |
| template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > |
(2) | (since C++20) |
Sorts the elements in the range [first, last) 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.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first, last | - | iterator-sentinel defining the range to sort |
| r | - | the range to sort |
| comp | - | comparison to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
An iterator equal to last.
Complexity
𝓞(N·log(N)) comparisons and projections, where N = ranges::distance(first, last).
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 {}; |
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)
Example
#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
See also
| (C++20) |
sorts the first N elements of a range (niebloid) |
| (C++20) |
sorts a range of elements while preserving order between equal elements (niebloid) |
| (C++20) |
divides a range of elements into two groups (niebloid) |
| sorts a range into ascending order (function template) |