[edit]Parameters

[edit]Return value

Iterator in the destination range, pointing past the last element copied ifcount>0 orresult otherwise.

[edit]Complexity

Zero assignments ifcount<0;count assignments otherwise.

[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

template<class InputIt,class Size,class OutputIt>constexpr//< since C++20OutputIt copy_n(InputIt first, Size count, OutputIt result){if(count>0){*result=*first;++result;for(Size i=1; i!= count;++i,(void)++result)*result=*++first;} return result;}

[edit]Example

#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';}

12345050

[edit]See also

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