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

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 the size of the uninitialized memory area.

[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, e.g. by using ranges::fill, if the value type of the output range is TrivialType.

[edit] Possible implementation

struct uninitialized_fill_fn { template<no-throw-forward-iterator I, no-throw-sentinel-for S, class T> requires std::constructible_from<std::iter_value_t, const T&> constexpr I operator()(I first, S last, const T& value) const { I rollback{first}; try { for (; !(first == last); ++first) ranges::construct_at(std::addressof(*first), value); return first; } catch (...) {
// rollback: destroy constructed elements for (; rollback != first; ++rollback) ranges::destroy_at(std::addressof(*rollback)); throw; } }   template<no-throw-forward-range R, class T> requires std::constructible_from<ranges::range_value_t, const T&> constexpr ranges::borrowed_iterator_t operator()(R&& r, const T& value) const { return (*this)(ranges::begin(r), ranges::end(r), value); } };   inline constexpr uninitialized_fill_fn uninitialized_fill{};

[edit] Example

#include #include #include   int main() { constexpr int n{4}; alignas(alignof(std::string)) char out[n * sizeof(std::string)];   try { auto first{reinterpret_cast<std::string*>(out)}; auto last{first + n}; std::ranges::uninitialized_fill(first, last, "▄▀▄▀▄▀▄▀");   int count{1}; for (auto it{first}; it != last; ++it) std::cout << count++ << ' ' << *it << '\n';   std::ranges::destroy(first, last); } catch(...) { std::cout << "Exception!\n"; } }

Output:

1 ▄▀▄▀▄▀▄▀ 2 ▄▀▄▀▄▀▄▀ 3 ▄▀▄▀▄▀▄▀ 4 ▄▀▄▀▄▀▄▀

[edit] Defect reports

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

[edit] See also