std::uninitialized_fill

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Memory management library

voidify

(exposition only*)

Allocators

allocator
allocator_traits (C++11)
allocation_result (C++23)
scoped_allocator_adaptor (C++11)
pmr::polymorphic_allocator (C++17)

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)

Uninitialized memory algorithms

uninitialized_copy
uninitialized_fill
uninitialized_move (C++17)
uninitialized_copy_n (C++11)
uninitialized_fill_n
uninitialized_move_n (C++17)
construct_at (C++20)

uninitialized_default_construct (C++17)
uninitialized_value_construct (C++17)
destroy (C++17)
uninitialized_default_construct_n (C++17)
uninitialized_value_construct_n (C++17)
destroy_n (C++17)
destroy_at (C++17)

Constrained uninitialized memory algorithms

ranges::uninitialized_copy (C++20)
ranges::uninitialized_fill (C++20)
ranges::uninitialized_move (C++20)
ranges::uninitialized_copy_n (C++20)
ranges::uninitialized_fill_n (C++20)
ranges::uninitialized_move_n (C++20)
ranges::construct_at (C++20)

ranges::uninitialized_default_construct (C++20)
ranges::uninitialized_value_construct (C++20)
ranges::destroy (C++20)
ranges::uninitialized_default_construct_n (C++20)
ranges::uninitialized_value_construct_n (C++20)
ranges::destroy_n (C++20)
ranges::destroy_at (C++20)

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::pool_options (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)

Explicit lifetime management
start_lifetime_as (C++23)
start_lifetime_as_array (C++23)

Types for composite class design
indirect (C++26)
polymorphic (C++26)

Uninitialized storage(until C++20)

raw_storage_iterator (until C++20*)
get_temporary_buffer (until C++20*)

return_temporary_buffer (until C++20*)

Garbage collector support(until C++23)

declare_reachable (C++11)(until C++23)
declare_no_pointers (C++11)(until C++23)
pointer_safety (C++11)(until C++23)

undeclare_reachable (C++11)(until C++23)
undeclare_no_pointers (C++11)(until C++23)
get_pointer_safety (C++11)(until C++23)

Low level memory
management

operator newoperator new[]

operator deleteoperator delete[]

(C++11)

(C++11)

(C++17)

(C++20)

(C++17)

(C++11)

(C++11)

(C++11)

(until C++17*)

(C++11)

(C++17)

(C++26)

(C++26)

enable_shared_from_this

(C++11)

(C++11)

(C++11)

(C++23)

(C++23)

(C++11)

(C++20)

(C++11)

(C++11)

(C++20)

is_sufficiently_aligned

(C++26)

C Library

malloc
calloc
realloc

free
aligned_alloc (C++17)

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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) Copiesvalue to an uninitialized memory area[first, last) as if by

for(; first!= last;++first)
::new(voidify(*first))
typenamestd::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 topolicy.

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

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.	(since C++20)

[edit]Parameters

first, last	-	the pair of iterators defining therange of elements to initialize
value	-	the value to construct the elements with
policy	-	theexecution policy to use
Type requirements
- `NoThrowForwardIt` must meet the requirements ofLegacyForwardIterator.
- 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 betweenfirst andlast.

[edit]Exceptions

The overload with a template parameter namedExecutionPolicy reports errors as follows:

If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, 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 forspecialized memory algorithms,(1)

[edit]Possible implementation

template<class NoThrowForwardIt,class T>constexprvoid uninitialized_fill(NoThrowForwardIt first, NoThrowForwardIt last,const T& value){using V=typenamestd::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(){conststd::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:

ExampleExampleExampleExample

[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 placementnew instead
LWG 2433	C++11	this algorithm might be hijacked by overloadedoperator&	usesstd::addressof
LWG 3870	C++20	this algorithm might create objects on aconst storage	kept disallowed

[edit]See also

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