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std::uninitialized_fill

Defined in header <memory>

Defined in header `<memory>`
template< class ForwardIt, class T > void uninitialized_fill( ForwardIt first, ForwardIt last, const T& value );	(1)
template< class ExecutionPolicy, class ForwardIt, class T > void uninitialized_fill( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, const T& value );	(2)	(since C++17)

template< class ForwardIt, class T >
void uninitialized_fill( ForwardIt first, ForwardIt last, const T& value );

(1)

template< class ExecutionPolicy, class ForwardIt, class T >
void uninitialized_fill( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, const T& value );

(2)

(since C++17)

1) Copies the given value to an uninitialized memory area, defined by the range [first, last) as if by

for (; first != last; ++first)
    ::new (/*VOIDIFY*/(*first))
        typename std::iterator_traits<ForwardIt>::value_type(value);

where /*VOIDIFY*/(e) is:

`static_cast<void*>(&e)`	(until C++11)
`static_cast<void*>(std::addressof(e))`	(since C++11) (until C++20)
`const_cast<void>(static_cast<const volatile void>(std::addressof(e)))`	(since C++20)

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 does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> (until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> (since C++20) is true.

Parameters

first, last	-	the range of the elements to initialize
value	-	the value to construct the elements with
policy	-	the execution policy to use. See execution policy for details.
Type requirements
-`ForwardIt` must meet the requirements of LegacyForwardIterator.
-No increment, assignment, comparison, or indirection through valid instances of `ForwardIt` may throw exceptions. Applying `&*` to a `ForwardIt` value must yield a pointer to its value type. (until C++11)

Return value

(none).

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.

Possible implementation

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

Example

#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>
 
int main()
{
    std::string* p;
    std::size_t sz;
    std::tie(p, sz) = std::get_temporary_buffer<std::string>(4);
 
    std::uninitialized_fill(p, p+sz, "Example");
 
    for (std::string* i = p; i != p+sz; ++i) {
        std::cout << *i << '\n';
        i->~basic_string<char>();
    }
    std::return_temporary_buffer(p);
}

Output:

Example
Example
Example
Example

uninitialized_fill_n	copies an object to an uninitialized area of memory, defined by a start and a count (function template)
ranges::uninitialized_fill (C++20)	copies an object to an uninitialized area of memory, defined by a range (niebloid)