| Constrained algorithms and algorithms on ranges(C++20) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Constrained algorithms, e.g.ranges::copy,ranges::sort, ... | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Numeric operations | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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std::ranges| Non-modifying sequence operations | |||||||||||||||||||||||||||||||||
| Modifying sequence operations | |||||||||||||||||||||||||||||||||
| Partitioning operations | |||||||||||||||||||||||||||||||||
| Sorting operations | |||||||||||||||||||||||||||||||||
| Binary search operations (on sorted ranges) | |||||||||||||||||||||||||||||||||
| Set operations (on sorted ranges) | |||||||||||||||||||||||||||||||||
| Heap operations | |||||||||||||||||||||||||||||||||
| Minimum/maximum operations | |||||||||||||||||||||||||||||||||
| Permutation operations | |||||||||||||||||||||||||||||||||
| Fold operations | |||||||||||||||||||||||||||||||||
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| Operations on uninitialized storage | |||||||||||||||||||||||||||||||||
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Defined in header <algorithm> | ||
Call signature | ||
template<std::input_iterator I,std::sentinel_for<I> S,std::weakly_incrementable O, std::copy_constructible F,class Proj=std::identity> | (1) | (since C++20) |
template<ranges::input_range R,std::weakly_incrementable O, std::copy_constructible F,class Proj=std::identity> | (2) | (since C++20) |
template<std::input_iterator I1,std::sentinel_for<I1> S1, std::input_iterator I2,std::sentinel_for<I2> S2, | (3) | (since C++20) |
template<ranges::input_range R1, ranges::input_range R2, | (4) | (since C++20) |
Helper types | ||
template<class I,class O> using unary_transform_result=ranges::in_out_result<I, O>; | (5) | (since C++20) |
template<class I1,class I2,class O> using binary_transform_result=ranges::in_in_out_result<I1, I2, O>; | (6) | (since C++20) |
Applies the given function to a range and stores the result in another range, beginning atresult.
[first1, last1) (after projecting with the projectionproj).[first1, last1) and the other defined by[first2, last2) (after respectively projecting with the projectionsproj1 andproj2).The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:
Contents |
| first1, last1 | - | the iterator-sentinel pair defining the firstrange of elements to transform |
| r, r1 | - | the first range of elements to transform |
| first2, last2 | - | the iterator-sentinel pair defining the secondrange of elements to transform |
| r2 | - | the second range of elements to transform |
| result | - | the beginning of the destination range, may be equal tofirst1 orfirst2 |
| op, binary_op | - | operation to apply to the projected element(s) |
| proj1 | - | projection to apply to the elements in the first range |
| proj2 | - | projection to apply to the elements in the second range |
unary_transform_result contains an input iterator equal tolast and an output iterator to the element past the last element transformed.binary_transform_result contains input iterators to last transformed elements from ranges[first1, last1) and[first2, last2) asin1 andin2 respectively, and the output iterator to the element past the last element transformed asout.struct transform_fn{// First versiontemplate<std::input_iterator I,std::sentinel_for<I> S,std::weakly_incrementable O,std::copy_constructible F,class Proj=std::identity> requiresstd::indirectly_writable<O,std::indirect_result_t<F&, std::projected<I, Proj>>>constexpr ranges::unary_transform_result<I, O> operator()(I first1, S last1, O result, F op, Proj proj={})const{for(; first1!= last1;++first1,(void)++result)*result=std::invoke(op,std::invoke(proj,*first1)); return{std::move(first1), std::move(result)};} // Second versiontemplate<ranges::input_range R,std::weakly_incrementable O,std::copy_constructible F,class Proj=std::identity> requiresstd::indirectly_writable<O,std::indirect_result_t<F&, std::projected<ranges::iterator_t<R>, Proj>>>constexpr ranges::unary_transform_result<ranges::borrowed_iterator_t<R>, O> operator()(R&& r, O result, F op, Proj proj={})const{return(*this)(ranges::begin(r),ranges::end(r), std::move(result), std::move(op), std::move(proj));} // Third versiontemplate<std::input_iterator I1,std::sentinel_for<I1> S1,std::input_iterator I2,std::sentinel_for<I2> S2,std::weakly_incrementable O,std::copy_constructible F,class Proj1=std::identity,class Proj2=std::identity> requiresstd::indirectly_writable<O,std::indirect_result_t<F&, std::projected<I1, Proj1>, std::projected<I2, Proj2>>>constexpr ranges::binary_transform_result<I1, I2, O> operator()(I1 first1, S1 last1, I2 first2, S2 last2, O result, F binary_op, Proj1 proj1={}, Proj2 proj2={})const{for(; first1!= last1&& first2!= last2;++first1,(void)++first2,(void)++result)*result=std::invoke(binary_op,std::invoke(proj1,*first1),std::invoke(proj2,*first2)); return{std::move(first1), std::move(first2), std::move(result)};} // Fourth versiontemplate<ranges::input_range R1,ranges::input_range R2,std::weakly_incrementable O,std::copy_constructible F,class Proj1=std::identity,class Proj2=std::identity> requiresstd::indirectly_writable<O,std::indirect_result_t<F&, std::projected<ranges::iterator_t<R1>, Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>>>constexpr ranges::binary_transform_result<ranges::borrowed_iterator_t<R1>,ranges::borrowed_iterator_t<R2>, O> operator()(R1&& r1, R2&& r2, O result, F binary_op, Proj1 proj1={}, Proj2 proj2={})const{return(*this)(ranges::begin(r1),ranges::end(r1),ranges::begin(r2),ranges::end(r2), std::move(result), std::move(binary_op), std::move(proj1), std::move(proj2));}}; inlineconstexpr transform_fn transform; |
ranges::transform does not guarantee in-order application ofop orbinary_op. To apply a function to a sequence in-order or to apply a function that modifies the elements of a sequence, useranges::for_each.
The following code usesranges::transform to convert a string in place to uppercase using thestd::toupper function and then transforms eachchar to its ordinal value.Thenranges::transform with a projection is used to transform elements ofstd::vector<Foo> into chars to fill astd::string.
#include <algorithm>#include <cctype>#include <functional>#include <iostream>#include <string>#include <vector> int main(){std::string s{"hello"};auto op=[](unsignedchar c)->unsignedchar{returnstd::toupper(c);}; namespace ranges= std::ranges; // uppercase the string in-place ranges::transform(s.begin(), s.end(), s.begin(), op); std::vector<std::size_t> ordinals;// convert each char to size_t ranges::transform(s,std::back_inserter(ordinals),[](unsignedchar c)->std::size_t{return c;}); std::cout<< s<<':';for(auto ord: ordinals)std::cout<<' '<< ord; // double each ordinal ranges::transform(ordinals, ordinals, ordinals.begin(),std::plus{}); std::cout<<'\n';for(auto ord: ordinals)std::cout<< ord<<' ';std::cout<<'\n'; struct Foo{char bar;};conststd::vector<Foo> f={{'h'},{'e'},{'l'},{'l'},{'o'}};std::string result;// project, then uppercase ranges::transform(f,std::back_inserter(result), op,&Foo::bar);std::cout<< result<<'\n';}
Output:
HELLO: 72 69 76 76 79144 138 152 152 158HELLO
(C++20) | applies a unaryfunction object to elements from arange (algorithm function object)[edit] |
aview of a sequence that applies a transformation function to each element(class template)(range adaptor object)[edit] | |
| applies a function to a range of elements, storing results in a destination range (function template)[edit] |
