std::fill_n - cppreference.com (original) (raw)

| Defined in header | | | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------------------------------- | | (1) | | | | template< class OutputIt, class Size, class T >OutputIt fill_n( OutputIt first, Size count, const T& value ); | | (constexpr since C++20) (until C++26) | | template< class OutputIt, class Size, class T = typename std::iterator_traits <OutputIt>::value_type > constexpr OutputIt fill_n( OutputIt first, Size count, const T& value ); | | (since C++26) | | (2) | | | | template< class ExecutionPolicy, class ForwardIt, class Size, class T >ForwardIt fill_n( ExecutionPolicy&& policy, ForwardIt first, Size count, const T& value ); | | (since C++17) (until C++26) | | template< class ExecutionPolicy, class ForwardIt, class Size, class T = typename std::iterator_traits <OutputIt>::value_type >ForwardIt fill_n( ExecutionPolicy&& policy, ForwardIt first, Size count, const T& value ); | | (since C++26) |

1. Assigns the given value to the first count elements in the range beginning at first if count > 0. Does nothing otherwise.

2. Same as (1), but executed according to policy.

This overload participates in overload resolution only if all following conditions are satisfied:

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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Possible implementation
• 6 Notes
• 7 Example
• 8 Defect reports
• 9 See also

[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

[edit] Notes

[edit] Example

#include #include #include #include #include   int main() { std::vector 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(std::cout, " ")); std::cout << '\n';   std::vector<std::complex> 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{4, 2}); #endif std::copy_n(nums.cbegin(), nums.size(), std::ostream_iterator<std::complex>(std::cout, " ")); std::cout << '\n'; }

Output:

-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

| | copy-assigns the given value to every element in a range (function template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | assigns a value to a number of elements(algorithm function object)[edit] |