std::adjacent_difference
Defined in header <numeric> |
||
---|---|---|
(1) | ||
template< class InputIt, class OutputIt > OutputIt adjacent_difference( InputIt first, InputIt last, OutputIt d_first ); |
(until C++20) | |
template< class InputIt, class OutputIt > constexpr OutputIt adjacent_difference( InputIt first, InputIt last, OutputIt d_first ); |
(since C++20) | |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt2 adjacent_difference( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first ); |
(2) | (since C++17) |
(3) | ||
template< class InputIt, class OutputIt, class BinaryOperation > OutputIt adjacent_difference( InputIt first, InputIt last, OutputIt d_first, BinaryOperation op ); |
(until C++20) | |
template< class InputIt, class OutputIt, class BinaryOperation > constexpr OutputIt adjacent_difference( InputIt first, InputIt last, OutputIt d_first, BinaryOperation op ); |
(since C++20) | |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryOperation > ForwardIt2 adjacent_difference( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, BinaryOperation op ); |
(4) | (since C++17) |
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 beginning at d_first + 1
. An unmodified copy of *first
is written to *d_first
.
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
.
*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
policy
. 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.
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); ...
|
(until C++11) |
|
(since C++11) |
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. |
op | - | binary operation function object that will be applied. The signature of the function should be equivalent to the following:
The signature does not need to have |
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 LegacyForwardIterator. 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::terminate
is called. For any otherExecutionPolicy
, 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
#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(begin(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
computes the partial sum of a range of elements (function template) |
|
sums up a range of elements (function template) |
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