std::ranges::uninitialized_fill_n - cppreference.com (original) (raw)

| Defined in header | | | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------------------------------- | | Call signature | | | | template< no-throw-forward-range I, class T > requires std::constructible_from<std::iter_value_t<I>, const T&>I uninitialized_fill_n( I first, std::iter_difference_t<I> count, const T& value ); | | (since C++20) (constexpr since C++26) |

Copies value to an uninitialized memory area first+ [​0​, count) as if byreturn ranges::uninitialized_fill(std::counted_iterator(first, count),
std::default_sentinel, value).base();

If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Contents

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

[edit] Parameters

[edit] Return value

As described above.

[edit] Complexity

Linear in count.

[edit] Exceptions

Any exception thrown on construction of the elements in the destination range.

[edit] Notes

An implementation may improve the efficiency of the ranges::uninitialized_fill_n, e.g. by using ranges::fill_n, if the value type of the output range is TrivialType.

[edit] Possible implementation

[edit] Example

#include #include #include   int main() { constexpr int n{3}; alignas(alignof(std::string)) char out[n * sizeof(std::string)];   try { auto first{reinterpret_cast<std::string*>(out)}; auto last = std::ranges::uninitialized_fill_n(first, n, "cppreference");   for (auto it{first}; it != last; ++it) std::cout << *it << '\n';   std::ranges::destroy(first, last); } catch (...) { std::cout << "Exception!\n"; } }

Output:

cppreference cppreference cppreference

[edit] Defect reports

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

[edit] See also