std::fill_n

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

• value is not writable to first.
• Size is not convertible to an integral type.

[edit] Parameters

[edit] Return value

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

[edit] Complexity

Exactly std::max (0, count) assignments.

[edit] 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 other ExecutionPolicy, 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 = typename std::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});
 #endif
 std::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