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std::uninitialized_fill

From cppreference.com
< cpp‎ | memory
 
C++
 
Memory management library
(exposition only*)
Allocators
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
(until C++20*)
(until C++20*)
(until C++20*)

Garbage collector support (until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
 
Defined in header <memory>
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:

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

Contents

[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

Feature-test macro Value Std Feature
__cpp_lib_raw_memory_algorithms 202411L (C++26) constexpr for specialized memory algorithms, (1)

[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

Run this code
#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
 
int main()
{
    const std::size_t sz = 4;
    std::allocator<std::string> alloc;