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std::copy_n

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Defined in header <algorithm>
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template< class InputIt, class Size, class OutputIt >
OutputIt copy_n( InputIt first, Size count, OutputIt result );
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Copies exactly count values from the range beginning at first to the range beginning at result, if count>0. Does nothing otherwise.

Contents

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
Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.

Return value

Iterator in the destination range, pointing past the last element copied if count>0 or first otherwise.

Complexity

Exactly count assignments, if count>0.

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

#include <iostream>
#include <string>
#include <algorithm>
#include <iterator>
 
int main()
{
    std::string in = "1234567890";
    std::string out;
 
    std::copy_n(in.begin(), 4, std::back_inserter(out));
    std::cout << out << '\n';
}

Output:

1234

See also

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