std::ranges::sort
From cppreference.com
| 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 >
requires std::sortable<I, Comp, Proj>
constexpr I
sort( I first, S last, Comp comp = {}, Proj proj = {} );
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(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 = {} );
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(2) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Comp = ranges::less, class Proj = std::identity >
requires std::sortable<I, Comp, Proj>
I sort( Ep&& policy, I first, S last, Comp comp = {}, Proj proj = {} );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Comp = ranges::less, class Proj = std::identity >
requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
ranges::borrowed_iterator_t<R>
sort( Ep&& policy, R&& r, Comp comp = {}, Proj proj = {} );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Sorts the elements in the target range
[first, last) or r with respect to the comparator comp and projection proj. The order of equivalent elements is not guaranteed to be preserved.3,4) Same as (1,2), but executed according to
policy.The function-like entities described on this page are algorithm function objects (informally known as 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.
Parameters
| first, last | - | the iterator-sentinel pair defining the target range |
| r | - | the target range |
| comp | - | the comparator to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
The past-the-end iterator of the target range.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1-4) 𝓞(N·log(N)) applications of
comp and proj.Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
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).
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::next(ranges::begin(r), ranges::end(r)),
std::move(comp), std::move(proj));
}
};
inline constexpr sort_fn sort{};
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Example
Run this code
#include <algorithm>
#include <array>
#include <functional>
#include <iomanip>
#include <iostream>
void print(auto comment, const auto& seq, char term = ' ')
{
for (std::cout << comment << '\n'; const auto& 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, const Particle& 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