std::uninitialized_fill
From cppreference.com
Defined in header <memory>
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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, |
(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:
|
(until C++11) |
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(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) |
Contents |
[edit] 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.
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-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)
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[edit] Return value
(none)
[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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] 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; } } |
[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; 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
[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 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 |
[edit] See also
copies an object to an uninitialized area of memory, defined by a start and a count (function template) | |
(C++20) |
copies an object to an uninitialized area of memory, defined by a range (niebloid) |