Constructs a sorted union beginning atresult consisting of the set of elements present in one or both sorted input ranges[first1, last1) and[first2, last2).

If some element is foundm times in[first1, last1) andn times in[first2, last2), then allm elements will be copied from[first1, last1) toresult, preserving order, and then exactlymax(n- m,0) elements will be copied from[first2, last2) toresult, also preserving order.

The behavior is undefined if

• the input ranges are not sorted with respect tocomp andproj1 orproj2, respectively, or
• the resulting range overlaps with either of the input ranges.

The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible toargument-dependent lookup.
• When any of them are found bynormal unqualified lookup as the name to the left of the function-call operator,argument-dependent lookup is inhibited.

[edit]Parameters

[edit]Return value

{last1, last2, result_last}, whereresult_last is the end of the constructed range.

[edit]Complexity

At most\(\scriptsize 2\cdot(N_1+N_2)-1\)2·(N1+N2)-1 comparisons and applications of each projection, where\(\scriptsize N_1\)N1 and\(\scriptsize N_2\)N2 areranges::distance(first1, last1) andranges::distance(first2, last2), respectively.

[edit]Notes

This algorithm performs a similar task asranges::merge does. Both consume two sorted input ranges and produce a sorted output with elements from both inputs. The difference between these two algorithms is with handling values from both input ranges which compare equivalent (see notes onLessThanComparable). If any equivalent values appearedn times in the first range andm times in the second,ranges::merge would output alln+m occurrences whereasranges::set_union would outputstd::max(n, m) ones only. Soranges::merge outputs exactly\(\scriptsize (N_1+N_2)\)(N1+N2) values andranges::set_union may produce less.

[edit]Possible implementation

struct set_union_fn{template<std::input_iterator I1,std::sentinel_for<I1> S1,std::input_iterator I2,std::sentinel_for<I2> S2,std::weakly_incrementable O,class Comp=ranges::less,class Proj1=std::identity,class Proj2=std::identity>    requiresstd::mergeable<I1, I2, O, Comp, Proj1, Proj2>constexpr ranges::set_union_result<I1, I2, O>        operator()(I1 first1, S1 last1, I2 first2, S2 last2,                   O result, Comp comp={},                   Proj1 proj1={}, Proj2 proj2={})const{for(;!(first1== last1 or first2== last2);++result){if(std::invoke(comp,std::invoke(proj1,*first1),std::invoke(proj2,*first2))){*result=*first1;++first1;}elseif(std::invoke(comp,std::invoke(proj2,*first2),std::invoke(proj1,*first1))){*result=*first2;++first2;}else{*result=*first1;++first1;++first2;}}auto res1=ranges::copy(std::move(first1), std::move(last1), std::move(result));auto res2=ranges::copy(std::move(first2), std::move(last2), std::move(res1.out));return{std::move(res1.in), std::move(res2.in), std::move(res2.out)};} template<ranges::input_range R1,ranges::input_range R2,std::weakly_incrementable O,class Comp=ranges::less,class Proj1=std::identity,class Proj2=std::identity>    requiresstd::mergeable<ranges::iterator_t<R1>,ranges::iterator_t<R2>,                            O, Comp, Proj1, Proj2>constexpr ranges::set_union_result<ranges::borrowed_iterator_t<R1>,ranges::borrowed_iterator_t<R2>, O>        operator()(R1&& r1, R2&& r2, O result, Comp comp={},                   Proj1 proj1={}, Proj2 proj2={})const{return(*this)(ranges::begin(r1),ranges::end(r1),ranges::begin(r2),ranges::end(r2),                       std::move(result), std::move(comp),                       std::move(proj1), std::move(proj2));}}; inlineconstexpr set_union_fn set_union{};

[edit]Example

#include <algorithm>#include <iostream>#include <iterator>#include <vector> void print(constauto& in1,constauto& in2,auto first,auto last){std::cout<<"{ ";for(constauto& e: in1)std::cout<< e<<' ';std::cout<<"} ∪ { ";for(constauto& e: in2)std::cout<< e<<' ';std::cout<<"} =\n{ ";while(!(first== last))std::cout<<*first++<<' ';std::cout<<"}\n\n";} int main(){std::vector<int> in1, in2, out;     in1={1,2,3,4,5};    in2={3,4,5,6,7};    out.resize(in1.size()+ in2.size());constauto ret= std::ranges::set_union(in1, in2, out.begin());    print(in1, in2, out.begin(), ret.out);     in1={1,2,3,4,5,5,5};    in2={3,4,5,6,7};    out.clear();    out.reserve(in1.size()+ in2.size());    std::ranges::set_union(in1, in2,std::back_inserter(out));    print(in1, in2, out.cbegin(), out.cend());}

{ 1 2 3 4 5 } ∪ { 3 4 5 6 7 } ={ 1 2 3 4 5 6 7 } { 1 2 3 4 5 5 5 } ∪ { 3 4 5 6 7 } ={ 1 2 3 4 5 5 5 6 7 }

[edit]See also

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文