Call signature
(1) (since C++20) (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.
1) Elements are compared using the given binary comparison function comp.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
An iterator equal to last.
[edit] Complexity\(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)ð(N·log(N)) comparisons and projections, where N = ranges::distance(first, last).
[edit] Possible implementationNote 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)
#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
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