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std::adjacent_difference(3) C++ Standard Libary std::adjacent_difference(3) NAME std::adjacent_difference - std::adjacent_difference Synopsis Defined in header <numeric> template< class InputIt, class OutputIt > OutputIt adjacent_difference( InputIt first, (until C++20) InputIt last, OutputIt d_first ); template< class InputIt, class OutputIt > constexpr OutputIt adjacent_difference( InputIt (since C++20) first, InputIt last, OutputIt d_first ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt2 adjacent_difference( (2) (since C++17) ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first ); template< class InputIt, class OutputIt, class BinaryOperation > (1) OutputIt adjacent_difference( InputIt first, (until C++20) InputIt last, OutputIt d_first, BinaryOperation op ); template< class InputIt, class OutputIt, class BinaryOperation > constexpr OutputIt adjacent_difference( InputIt (since C++20) first, InputIt last, (3) OutputIt d_first, BinaryOperation op ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryOperation > ForwardIt2 adjacent_difference( (4) (since C++17) ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, BinaryOperation op ); Computes the differences between the second and the first of each adjacent pair of elements of the range [first, last) and writes them to the range be- ginning at d_first + 1. An unmodified copy of *first is written to *d_first. 1,3) First, creates an accumulator acc whose type is InputIt's value type, initializes it with *first, and assigns the result to *d_first. Then, for every iterator i in [first + 1, last) in order, creates an object val whose type is InputIt's value type, initializes it with *i, computes val - acc (until C++20) val - std::move(acc) (since C++20) (overload (1)) or op(val, acc) (until C++20) op(val, std::move(acc)) (since C++20) (overload (3)), assigns the result to *(d_first + (i - first)), and move assigns from val to acc. first may be equal to d_first. 2,4) Performs *d_first = *first;. For every d in [1, last - first - 1], assigns *(first + d) - *(first + d - 1) (overload (2)) or op(*(first + d), *(first + d - 1)) (overload (4)) to *(d_first + d). This is executed according to pol- icy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> (until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> (since C++20) is true. The behavior is undefined if the input and output ranges overlap in any way. Equivalent operation: *(d_first) = *first; *(d_first+1) = *(first+1) - *(first); *(d_first+2) = *(first+2) - *(first+1); *(d_first+3) = *(first+3) - *(first+2); ... op must not have side effects. (until C++11) op must not invalidate any iterators, including the end iterators, or (since C++11) modify any elements of the ranges involved. Parameters first, last - the range of elements d_first - the beginning of the destination range policy - the execution policy to use. See execution policy for details. binary operation function object that will be ap- plied. The signature of the function should be equivalent to the following: Ret fun(const Type1 &a, const Type2 &b); op - The signature does not need to have const &. The types Type1 and Type2 must be such that an ob- ject of type iterator_traits<InputIt>::value_type can be implic- itly converted to both of them. The type Ret must be such that an ob- ject of type OutputIt can be dereferenced and assigned a value of type Ret. Type requirements - InputIt must meet the requirements of LegacyInputIterator. InputIt's value type must be MoveAssignable and constructible from the type of *first - OutputIt must meet the requirements of LegacyOutputIterator. both acc (the accumulated value) and the result of val - acc or op(val, acc) (until C++20) val - std::move(acc) or op(val, std::move(acc)) (since C++20) must be writable to OutputIt - ForwardIt1, ForwardIt2 must meet the requirements of LegacyFor- wardIterator. The results of *first, *first - *first (for (2)) and op(*first, *first) (for (4)) must be writable to ForwardIt2. Return value Iterator to the element past the last element written. Notes If first == last, this function has no effect and will merely return d_first. Complexity Exactly (last - first) - 1 applications of the binary operation Exceptions The overloads with a template parameter named ExecutionPolicy report errors as follows: * If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::termi- nate is called. For any other ExecutionPolicy, the behavior is implementation- defined. * If the algorithm fails to allocate memory, std::bad_alloc is thrown. Possible implementation First version template<class InputIt, class OutputIt> constexpr // since C++20 OutputIt adjacent_difference(InputIt first, InputIt last, OutputIt d_first) { if (first == last) return d_first; typedef typename std::iterator_traits<InputIt>::value_type value_t; value_t acc = *first; *d_first = acc; while (++first != last) { value_t val = *first; *++d_first = val - std::move(acc); // std::move since C++20 acc = std::move(val); } return ++d_first; } Second version template<class InputIt, class OutputIt, class BinaryOperation> constexpr // since C++20 OutputIt adjacent_difference(InputIt first, InputIt last, OutputIt d_first, BinaryOperation op) { if (first == last) return d_first; typedef typename std::iterator_traits<InputIt>::value_type value_t; value_t acc = *first; *d_first = acc; while (++first != last) { value_t val = *first; *++d_first = op(val, std::move(acc)); // std::move since C++20 acc = std::move(val); } return ++d_first; } Example // Run this code #include <numeric> #include <vector> #include <array> #include <iostream> #include <functional> #include <iterator> auto print = [](auto comment, auto const& sequence) { std::cout << comment; for (const auto& n : sequence) std::cout << n << ' '; std::cout << '\n'; }; int main() { // Default implementation - the difference b/w two adjacent items std::vector v {4, 6, 9, 13, 18, 19, 19, 15, 10}; print("Initially, v = ", v); std::adjacent_difference(v.begin(), v.end(), v.begin()); print("Modified v = ", v); // Fibonacci std::array<int, 10> a {1}; adjacent_difference(begin(a), std::prev(end(a)), std::next(be- gin(a)), std::plus<> {}); print("Fibonacci, a = ", a); } Output: Initially, v = 4 6 9 13 18 19 19 15 10 Modified v = 4 2 3 4 5 1 0 -4 -5 Fibonacci, a = 1 1 2 3 5 8 13 21 34 55 See also partial_sum computes the partial sum of a range of elements (function template) accumulate sums up a range of elements (function template) http://cppreference.com 2022.07.31 std::adjacent_difference(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Notes | Complexity | Exceptions | Possible implementation | First version | Second version | Example | Output: | See also
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