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std::uninitialized_fill - cppreference.com

template< class NoThrowForwardIt, class T > void uninitialized_fill( NoThrowForwardIt first, NoThrowForwardIt last, const T& value ); (1) (constexpr since C++26) template< class ExecutionPolicy, class NoThrowForwardIt, class T > void uninitialized_fill( ExecutionPolicy&& policy, NoThrowForwardIt first, NoThrowForwardIt last, const T& value ); (2) (since C++17) 1)

Copies

value

to an uninitialized memory area

[first, last)

as if by

for (; first != last; ++first) ::new (voidify(*first)) typename std::iterator_traits<NoThrowForwardIt>::value_type(value);

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

2) Same as (1), but executed according to policy.

This overload participates in overload resolution only if all following conditions are satisfied:

[edit] Parameters first, last - the pair of iterators defining the range of elements to initialize value - the value to construct the elements with policy - the execution policy to use Type requirements -NoThrowForwardIt must meet the requirements of LegacyForwardIterator. -No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions. Applying &* to a NoThrowForwardIt value must yield a pointer to its value type.(until C++11) [edit] Complexity

Linear in the distance between first and last.

[edit] 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.

[edit] Notes [edit] Possible implementation

template<class NoThrowForwardIt, class T>
constexpr void uninitialized_fill(NoThrowForwardIt first, NoThrowForwardIt last,
                                  const T& value)
{
    using V = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = first;
    try
    {
        for (; current != last; ++current)
            ::new (static_cast<void*>(std::addressof(*current))) V(value);
    } 
    catch (...)
    {
        for (; first != current; ++first)
            first->~V();
        throw;
    }
}

[edit] Example

#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
 
int main()
{
    const std::size_t sz = 4;
    std::allocator<std::string> alloc;
    std::string* p = alloc.allocate(sz);
 
    std::uninitialized_fill(p, p + sz, "Example");
 
    for (std::string* i = p; i != p + sz; ++i)
    {
        std::cout << *i << '\n';
        i->~basic_string<char>();
    }
 
    alloc.deallocate(p, sz);
}

Output:

Example
Example
Example
Example

[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 866 C++98 given T as the value type of NoThrowForwardIt, if
T::operator new exists, the program might be ill-formed uses global placement new instead LWG 2433 C++11 this algorithm might be hijacked by overloaded operator& uses std::addressof LWG 3870 C++20 this algorithm might create objects on a const storage kept disallowed [edit] See also

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