std::copy_n
From cppreference.com
Defined in header <algorithm>
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(1) | ||
template< class InputIt, class Size, class OutputIt > OutputIt copy_n( InputIt first, Size count, OutputIt result ); |
(since C++11) (until C++20) |
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template< class InputIt, class Size, class OutputIt > constexpr OutputIt copy_n( InputIt first, Size count, OutputIt result ); |
(since C++20) | |
template< class ExecutionPolicy, class ForwardIt1, class Size, class ForwardIt2 > ForwardIt2 copy_n( ExecutionPolicy&& policy, ForwardIt1 first, Size count, ForwardIt2 result ); |
(2) | (since C++17) |
1) Copies exactly
count
values from the range beginning at first
to the range beginning at result
. Formally, for each integer 0 ≤ i < count
, performs *(result + i) = *(first + i). Overlap of ranges is formally permitted, but leads to unpredictable ordering of the results.2) Same as (1), but executed according to
policy
. This overload does 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.Parameters
first | - | the beginning of the range of elements to copy from |
count | - | number of the elements to copy |
result | - | the beginning of the destination range |
policy | - | the execution policy to use. See execution policy for details. |
Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
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-OutputIt must meet the requirements of LegacyOutputIterator.
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-ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
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Return value
Iterator in the destination range, pointing past the last element copied if count>0
or result
otherwise.
Complexity
Zero assignments if count < 0
; count
assignments otherwise.
Exceptions
The overload with a template parameter named ExecutionPolicy
reports 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
template< class InputIt, class Size, class OutputIt> OutputIt copy_n(InputIt first, Size count, OutputIt result) { if (count > 0) { *result++ = *first; for (Size i = 1; i < count; ++i) { *result++ = *++first; } } return result; } |
Example
Run this code
#include <algorithm> #include <iostream> #include <iterator> #include <numeric> #include <string> #include <vector> int main() { std::string in = "1234567890"; std::string out; std::copy_n(in.begin(), 4, std::back_inserter(out)); std::cout << out << '\n'; std::vector<int> v_in(128); std::iota(v_in.begin(), v_in.end(), 1); std::vector<int> v_out(v_in.size()); std::copy_n(v_in.cbegin(), 100, v_out.begin()); std::cout << std::accumulate(v_out.begin(), v_out.end(), 0) << '\n'; }
Output:
1234 5050
See also
(C++11) |
copies a range of elements to a new location (function template) |
(C++20) |
copies a number of elements to a new location (niebloid) |