std::uninitialized_fill
From cppreference.com
| 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, |
(2) | (since C++17) |
1) Copies the given value to an uninitialized memory area, defined by the range
::new (/* VOIDIFY */(*first))
typename std::iterator_traits<ForwardIt>::value_type(value);
[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) |
|
(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 participates in overload resolution only if
|
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
ExecutionPolicyis 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.
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 866 | C++98 | given T as the value type of ForwardIt, ifT::operator new exists, the program might be ill-formed |
uses global replacement- new instead |
| 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
| 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) |