std:: uninitialized_value_construct

Parameters

Complexity

Linear in the distance between first and last .

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.

Notes

Possible implementation

template<class NoThrowForwardIt>
constexpr void uninitialized_value_construct(NoThrowForwardIt first,
                                             NoThrowForwardIt last)
{
    using Value = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = first;
    try
    {
        for (; current != last; ++current)
        {
            ::new (static_cast<void*>(std::addressof(*current))) Value();
        }
    }
    catch (...)
    {
        std::destroy(first, current);
        throw;
    }
}

Example

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

Default value
Default value
Default value
1 2 3 4
0 0 0 0

Defect reports

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

See also