std::reverse_copy

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Constrained algorithms and algorithms on ranges(C++20)

Constrained algorithms, e.g.ranges::copy,ranges::sort, ...

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(C++17)

execution::seqexecution::parexecution::par_unseqexecution::unseq

(C++17) (C++17)(C++17)(C++20)

execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced

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uninitialized_default_construct (C++17)
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uninitialized_default_construct_n (C++17)
uninitialized_value_construct_n (C++17)

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Defined in header`<algorithm>`
template<class BidirIt,class OutputIt> OutputIt reverse_copy( BidirIt first, BidirIt last, OutputIt d_first);	(1)	(constexpr since C++20)
template<class ExecutionPolicy,class BidirIt,class ForwardIt> ForwardIt reverse_copy( ExecutionPolicy&& policy, BidirIt first, BidirIt last, ForwardIt d_first);	(2)	(since C++17)

1) Given\(\scriptsize N\)N asstd::distance(first, last). Copies the elements from the range[first, last) (source range) to another range of\(\scriptsize N\)N elements beginning atd_first (destination range) in such a way that the elements in the destination range are in reverse order.

Behaves as if by executing the assignment*(d_first+ N-1- i)=*(first+ i)^[1] once for each integeri in[0, N).

If source and destination ranges overlap, the behavior is undefined.

2) Same as(1), but executed according topolicy.

This overload participates in overload resolution only if all following conditions are satisfied:

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.	(since C++20)

[edit]Parameters

first, last	-	the pair of iterators defining the sourcerange of elements to copy
d_first	-	the beginning of the destination range
Type requirements
- `BidirIt` must meet the requirements ofLegacyBidirectionalIterator.
- `OutputIt` must meet the requirements ofLegacyOutputIterator.
- `ForwardIt` must meet the requirements ofLegacyForwardIterator.

[edit]Return value

Output iterator to the element past the last element copied.

[edit]Complexity

Exactly\(\scriptsize N\)N assignments.

[edit]Exceptions

The overload with a template parameter namedExecutionPolicy reports errors as follows:

If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard 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.

[edit]Possible implementation

See also the implementations inlibstdc++,libc++, andMSVC STL.

template<class BidirIt,class OutputIt>constexpr// since C++20OutputIt reverse_copy(BidirIt first, BidirIt last, OutputIt d_first){for(; first!= last;++d_first)*d_first=*(--last);return d_first;}

[edit]Notes

Implementations (e.g.MSVC STL) may enable vectorization when the both iterator types satisfyLegacyContiguousIterator and have the same value type, and the value type isTriviallyCopyable.

[edit]Example

Run this code

#include <algorithm>#include <iostream>#include <vector> int main(){auto print=[](conststd::vector<int>& v){for(constauto& value: v)std::cout<< value<<' ';std::cout<<'\n';}; std::vector<int> v{1,2,3};    print(v); std::vector<int> destination(3);    std::reverse_copy(std::begin(v),std::end(v),std::begin(destination));    print(destination);     std::reverse_copy(std::rbegin(v),std::rend(v),std::begin(destination));    print(destination);}

Output:

1 2 3 3 2 1 1 2 3

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2074	C++98	for eachi, the assignment was (d_first+ N- i)=(first+ i)^[1]	corrected to (d_first+ N-1- i)=(first+ i)^[1]
LWG 2150	C++98	only one element was required to be assigned	corrected the requirement

↑^1.0^1.1^1.2LegacyOutputIterator is not required to support binary+ and-. The usages of+ and- here are exposition-only: the actual computation does not need to use them.

[edit]See also

reverse	reverses the order of elements in a range (function template)[edit]
ranges::reverse_copy (C++20)	creates a copy of a range that is reversed (algorithm function object)[edit]