std::ranges::uninitialized_value_construct - 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 distance between first and last.

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

[edit] Possible implementation

[edit] Example

#include #include #include   int main() { struct S { std::string m{"▄▀▄▀▄▀▄▀"}; };   constexpr int n{4}; alignas(alignof(S)) char out[n * sizeof(S)];   try { auto first{reinterpret_cast<S*>(out)}; auto last{first + n};   std::ranges::uninitialized_value_construct(first, last);   auto count{1}; for (auto it{first}; it != last; ++it) std::cout << count++ << ' ' << it->m << '\n';   std::ranges::destroy(first, last); } catch (...) { std::cout << "Exception!\n"; }   // For scalar types, uninitialized_value_construct // zero-fills the given uninitialized memory area. int v[]{0, 1, 2, 3}; std::cout << ' '; for (const int i : v) std::cout << ' ' << static_cast(i + 'A'); std::cout << "\n "; std::ranges::uninitialized_value_construct(std::begin(v), std::end(v)); for (const int i : v) std::cout << ' ' << static_cast(i + 'A'); std::cout << '\n'; }

Output:

1 ▄▀▄▀▄▀▄▀ 2 ▄▀▄▀▄▀▄▀ 3 ▄▀▄▀▄▀▄▀ 4 ▄▀▄▀▄▀▄▀ A B C D A A A A

[edit] Defect reports

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

[edit] See also