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Showing content from https://en.cppreference.com/w/cpp/language/../memory/ranges/uninitialized_value_construct.html below:

std::ranges::uninitialized_value_construct - cppreference.com

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.

[edit] Parameters first, last - the iterator-sentinel pair defining the range of elements to value-initialize r - the range of the elements to value-initialize [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 <iostream>
#include <memory>
#include <string>
 
int main()
{
    struct S { std::string m{"ââââââââ"}; };
 
    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<char>(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<char>(i + 'A');
    std::cout << '\n';
}

Output:

1 ââââââââ
2 ââââââââ
3 ââââââââ
4 ââââââââ
  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.

DR Applied to Behavior as published Correct behavior LWG 3870 C++20 this algorithm might create objects on a const storage kept disallowed [edit] See also

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