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std::ranges::stable_sort(3) C++ Standard Libary std::ranges::stable_sort(3) NAME std::ranges::stable_sort - std::ranges::stable_sort Synopsis 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 (since C++20) > (1) (constexpr since requires std::sortable<I, Comp, Proj> C++26) I stable_sort( I first, S last, Comp comp = {}, Proj proj = {} ); template< ranges::random_access_range R, class Comp = ranges::less, (since C++20) class Proj = std::identity > (2) (constexpr since requires std::sortable<ranges::iterator_t<R>, Comp, Proj> C++26) ranges::borrowed_iterator_t<R> stable_sort( R&& r, Comp comp = {}, Proj proj = {} ); Sorts the elements in the range [first, last) in non-descending or- der. The order of equivalent elements is stable, i.e. 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 range, as if using ranges::be- gin(r) as first and ranges::end(r) as last. The function-like entities described on this page are niebloids, that is: * Explicit template argument lists cannot be specified when call- ing 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 in- hibited. 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 \(\scriptsize N\cdot\log{(N)}\)Nlog(N) comparisons, if extra memory is available; where \(\scriptsize N\)N is ranges::distance(first, last). \(\scriptsize N\cdot\log^2{(N)}\)Nlog(N) comparisons otherwise. Twice as many pro- jections as the number of comparisons in both cases. Notes Feature-test macro Value Std Feature __cpp_lib_constexpr_algorithms 202306L constexpr stable sorting Possible implementation This implementation only shows the slower algorithm used when no ad- ditional memory is available. See also implementation in MSVC STL and libstdc++. struct stable_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 //< since C++26 I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { auto count = ranges::distance(first, last); auto mid = first + count / 2; auto last_it = first + count; if (count <= 1) return last_it; (*this)(first, mid, std::ref(comp), std::ref(proj)); (*this)(mid, last_it, std::ref(comp), std::ref(proj)); ranges::inplace_merge(first, mid, last_it); return last_it; } template<ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity> requires std::sortable<ranges::iterator_t<R>, Comp, Proj> constexpr //< since C++26 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 stable_sort_fn stable_sort {}; Example // Run this code #include <algorithm> #include <array> #include <functional> #include <iomanip> #include <iostream> void print(auto const& seq) { for (auto const& elem : seq) std::cout << elem << ' '; std::cout << '\n'; } struct Particle { std::string name; double mass; // MeV friend std::ostream& operator<<(std::ostream& os, Particle const& p) { return os << '\n' << std::left << std::setw(8) << p.name << " : " << p.mass; } }; int main() { std::array s {5, 7, 4, 2, 8, 6, 1, 9, 0, 3}; // sort using the default operator< std::ranges::stable_sort(s); print(s); // sort using a standard library compare function object std::ranges::stable_sort(s, std::ranges::greater()); print(s); // sort using a custom function object struct { bool operator()(int a, int b) const { return a < b; } } customLess; std::ranges::stable_sort(s.begin(), s.end(), customLess); print(s); // sort using a lambda expression std::ranges::stable_sort(s, [](int a, int b) { return a > b; }); print(s); // sort with projection Particle particles[] { {"Electron", 0.511}, {"Muon", 105.66}, {"Tau", 1776.86}, {"Positron", 0.511}, {"Proton", 938.27}, {"Neutron", 939.57} }; print(particles); std::ranges::stable_sort(particles, {}, &Particle::name); //< sort by name print(particles); std::ranges::stable_sort(particles, {}, &Particle::mass); //< sort by mass print(particles); } Output: 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0 Electron : 0.511 Muon : 105.66 Tau : 1776.86 Positron : 0.511 Proton : 938.27 Neutron : 939.57 Electron : 0.511 Muon : 105.66 Neutron : 939.57 Positron : 0.511 Proton : 938.27 Tau : 1776.86 Electron : 0.511 Positron : 0.511 Muon : 105.66 Proton : 938.27 Neutron : 939.57 Tau : 1776.86 See also ranges::sort sorts a range into ascending order (C++20) (niebloid) ranges::partial_sort sorts the first N elements of a range (C++20) (niebloid) ranges::stable_partition divides elements into two groups while pre- serving their (C++20) relative order (niebloid) sorts a range of elements while preserving order between stable_sort equal elements (function template) http://cppreference.com 2024.06.10 std::ranges::stable_sort(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Possible implementation | Example | Output: | See also
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