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std::uninitialized_fill

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)

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)

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

for (; first != last; ++first)
  ::new (static_cast<void*>(std::addressof(*first)))
      typename iterator_traits<ForwardIt>::value_type(x);

If an exception is thrown during the initialization, the function has no effects.

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>> 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 `ForwardIterator`.
-No increment, assignment, comparison, or indirection through valid instances of `ForwardIt` may throw exceptions.

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, std::terminate is called.
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)
{
    typedef typename std::iterator_traits<ForwardIt>::value_type Value;
    ForwardIt current = first;
    try {
        for (; current != last; ++current) {
            ::new (static_cast<void*>(std::addressof(*current))) Value(value);
        }
    }  catch (...) {
        for (; first != current; ++first) {
            first->~Value();
        }
        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)
std::experimental::parallel::uninitialized_fill (parallelism TS)	parallelized version of `std::uninitialized_fill` (function template)