std::uninitialized_fill

 

C++

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Freestanding and hosted

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Symbols index

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General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

Dynamic memory management

Smart pointers unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (until C++17) owner_less (C++11) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) out_ptr_t (C++23) inout_ptr_t (C++23) Allocators allocator allocator_traits (C++11) allocation_result (C++23) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20)   scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) pmr::pool_options (C++17) Uninitialized storage raw_storage_iterator (until C++20) get_temporary_buffer (until C++20) return_temporary_buffer (until C++20)

Uninitialized memory algorithms uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) destroy_at (C++17) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) construct_at (C++20) Constrained uninitialized memory algorithms ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::uninitialized_default_construct (C++20)   ranges::uninitialized_value_construct (C++20) ranges::destroy (C++20) ranges::destroy_at (C++20) ranges::uninitialized_copy_n (C++20) ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::uninitialized_default_construct_n (C++20) ranges::uninitialized_value_construct_n (C++20) ranges::destroy_n (C++20) ranges::construct_at (C++20) Garbage collection support declare_reachable (C++11)(until C++23) undeclare_reachable (C++11)(until C++23) declare_no_pointers (C++11)(until C++23) undeclare_no_pointers (C++11)(until C++23) pointer_safety (C++11)(until C++23) get_pointer_safety (C++11)(until C++23) Miscellaneous pointer_traits (C++11) to_address (C++20) addressof (C++11) align (C++11) assume_aligned (C++20) C Library malloc aligned_alloc (C++17) calloc realloc free Low level memory management operator new operator new[] operator delete operator delete[] get_new_handler set_new_handler launder (C++17) bad_alloc bad_array_new_length nothrow_t align_val_t destroying_delete_t new_handler nothrow

 

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 (/*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)

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>> is true.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.	(since C++20)

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 (static_cast<void*>(std::addressof(*current))) V(value); } catch (...) { for (; first != current; ++first) first->~V(); throw; } }

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;
    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

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 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

See also

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)