If any of the following conditions is satisfied, the program is ill-formed:

• value is notwritable tofirst.
• Size is notconvertible to anintegral type.

[edit]Parameters

[edit]Return value

Iterator one past the last element assigned ifcount>0,first otherwise.

[edit]Complexity

Exactlystd::max(0, count) 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

template<class OutputIt,class Size,class T=typenamestd::iterator_traits<OutputIt>::value_type>OutputIt fill_n(OutputIt first, Size count,const T& value){for(Size i=0; i< count; i++)*first++= value;return first;}

[edit]Notes

[edit]Example

#include <algorithm>#include <complex>#include <iostream>#include <iterator>#include <vector> int main(){std::vector<int> v1{0,1,2,3,4,5,6,7,8,9}; // replace values of the first 5 elements with -1    std::fill_n(v1.begin(),5,-1); std::copy_n(v1.cbegin(), v1.size(),std::ostream_iterator<int>(std::cout," "));std::cout<<'\n'; std::vector<std::complex<double>> nums{{1,3},{2,2},{4,8}};#ifdef __cpp_lib_algorithm_default_value_type        std::fill_n(nums.begin(),2,{4,2});#else        std::fill_n(nums.begin(),2,std::complex<double>{4,2});#endifstd::copy_n(nums.cbegin(), nums.size(),std::ostream_iterator<std::complex<double>>(std::cout," "));std::cout<<'\n';}

-1 -1 -1 -1 -1 5 6 7 8 9(4,2) (4,2) (4,8)

[edit]Defect reports

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

[edit]See also

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