Merges twosorted ranges[[first1, last1) and[first2, last2) into onesorted range beginning atresult.

A sequence is said to besorted with respect to the comparatorcomp if for any iteratorit pointing to the sequence and any non-negative integern such thatit + n is a valid iterator pointing to an element of the sequence,std::invoke(comp,std::invoke(proj2,*(it+ n)),std::invoke(proj1,*it))) evaluates tofalse.

The behavior is undefined if the destination range overlaps either of the input ranges (the input ranges may overlap each other).

This merge function isstable, which means that for equivalent elements in the original two ranges, the elements from the first range (preserving their original order) precede the elements from the second range (preserving their original order).

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 mostN −1 comparisons and applications of each projection, whereN=ranges::distance(first1, last1)+ranges::distance(first2, last12).

[edit]Notes

This algorithm performs a similar task asranges::set_union 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 outputmax(n, m) ones only. Soranges::merge outputs exactlyN values andranges::set_union may produce fewer.

[edit]Possible implementation

struct merge_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::merge_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(proj2,*first2),std::invoke(proj1,*first1)))*result=*first2,++first2;else*result=*first1,++first1;}auto ret1{ranges::copy(std::move(first1), std::move(last1), std::move(result))};auto ret2{ranges::copy(std::move(first2), std::move(last2), std::move(ret1.out))};return{std::move(ret1.in), std::move(ret2.in), std::move(ret2.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::merge_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 merge_fn merge{};

[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<<"} +\n{ ";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::merge(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::merge(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 3 4 4 5 5 6 7 } { 1 2 3 4 5 5 5 } +{ 3 4 5 6 7 } ={ 1 2 3 3 4 4 5 5 5 5 6 7 }

[edit]See also

• In other languages

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